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This Mashed Potato Casserole Recipe combines fluffy Russet potatoes with butter, heavy cream, sour cream, and sharp cheddar cheese. Topped with even more cheddar and baked until hot and melty, it’s a rich, creamy, and comforting side dish that’s perfect for Thanksgiving, Christmas, and family dinners. Plus, it can be made ahead!
This easy, make-ahead mashed potato casserole is one of my favorite sides to bring to holiday dinners and potlucks. It’s a cross between my classic mashed potatoes and the creamy, cheesy filling of my twice baked potatoes, only without the extra work of scooping and stuffing individual potato skins. To make it, we’re mashing fluffy Russet potatoes with butter, whole milk, heavy cream, sour cream, and shredded cheddar. Everything goes into a baking dish with another generous layer of cheddar on top and gets baked until hot and melty. The result is rich, creamy, and absolutely delicious – perfect for feeding a crowd.
The best part? You can assemble the entire casserole up to two days ahead of time, and it travels well. Basically, one less thing to worry about when getting ready for a big holiday meal.
Quick Look: Make-Ahead Mashed Potato Casserole
- Servings: Approximately 12 side-dish servings, making it a great option for holiday dinners, potlucks, and feeding a crowd.
- Total Time: Plan on approximately 1 hour 30 minutes from start to finish, including 25 minutes in the oven at 375°F. If the casserole has been refrigerated, expect that it will need an additional 15-25 minutes in the oven.
- Tools and Equipment: You’ll need a large pot or Dutch oven, colander, potato masher, cheese grater, and a 9×13-inch baking dish.
- Making Ahead: Assemble the casserole up to 2 days in advance. Double the whole milk from 3/4 cup to 1 1/2 cups total to help keep the potatoes creamy after refrigeration. Take it out of the refrigerator about an hour before baking.
- Top Tip: Add the butter to the hot potatoes before mixing in the warm milk and cream. This helps keep the potatoes creamy, while avoiding overmixing prevents them from becoming gummy. You’re looking for a thick, creamy consistency that’s still soft enough to spread easily.
- Leftovers: Refrigerate for up to 4 days. Add a splash of milk when reheating to bring back some of that creaminess, or put the leftovers to good use in something like shepherd’s pie.
Table of Contents
Ingredients and Substitutions
This mashed potato casserole is made with simple ingredients, most of which you probably already have on hand. Here’s what you’ll need, along with a few helpful substitutions.
- Russet potatoes: I recommend making this casserole dish with Russet potatoes. Considered “starchy potatoes,” they result in light, fluffy mashed potatoes. All-purpose potatoes, like Yukon Gold, are a good alternative, but they’ll give the casserole a slightly denser, creamier texture. I would avoid waxy red potatoes for this recipe. Confused about what it means to be a starchy, waxy, or all-purpose potato? Check out my post, Starchy vs. Waxy Potatoes, where I explain their differences and outline when to use each.
- Butter: One full stick of butter adds richness and flavor. I like to add it directly to the hot potatoes before mixing in the milk and cream. This helps coat the potato starch with fat, giving the mashed potatoes a smoother, creamier texture.
- Heavy cream and whole milk: The combination gives the potatoes their rich, creamy consistency without making them overly heavy. Bring both to room temperature, or gently heat them on the stovetop, before mixing them into the potatoes. Half-and-half can replace the heavy cream if needed, although the result will be a little less rich. Important: If you’re making the casserole ahead of time, increase the whole milk from 3/4 cup to 1 1/2 cups total to help keep the potatoes creamy after refrigeration.
- Sour Cream: We’re using a full 16-ounce container of full-fat sour cream, and for good reason. Just like a generous dollop of sour cream on a perfectly baked potato, it adds a little tang that balances the richness of the butter and cream. That generous amount also helps give the mashed potatoes a thicker, creamier consistency and helps prevent them from feeling dry.
- Sharp Cheddar Cheese: Freshly shredded sharp cheddar adds plenty of cheesy flavor without overpowering the potatoes. You’ll mix 1 cup into the mashed potatoes and sprinkle the remaining 1 1/2 cups over the top before baking. Medium cheddar also works if you prefer a milder flavor. I recommend shredding your own cheese for the smoothest melt.
- Green Onions: Add a mild onion flavor and a little color. You can substitute fresh chives or leave them out if you prefer.
- Salt and Black Pepper: Potatoes need plenty of seasoning, especially with all that dairy. I start with 2 teaspoons of salt and 1 teaspoon of black pepper, adding more to taste before transferring them to the baking dish.
Optional Bacon: If you love loaded mashed potatoes, feel free to add some crispy, crumbled bacon! Fold it into the potatoes with the cheddar and green onions, or sprinkle it over the finished casserole for a little crunch. For an easy way to prepare it, try my oven-baked bacon or air fryer bacon recipes.
How to Make Mashed Potato Casserole
- Boil the potatoes. Peel the Russet potatoes and cut them into approximately 2-inch pieces. Transfer to a large pot or Dutch oven and cover with cold, salted water by about 1 inch. Bring to a boil, then reduce the heat slightly and simmer for 15-20 minutes, or until the potatoes are completely fork-tender.
- Drain and add the butter. Drain the potatoes thoroughly in a large colander, then return them to the warm pot. Let them sit for a minute or two to allow steam to evaporate. Add the cold butter, cut into pieces, directly to the hot potatoes.
- Mash the potatoes. Using a potato masher, gently mash the potatoes and butter until most of the larger lumps are gone. Gradually pour in the whole milk and heavy cream, continuing to mash until incorporated. Don’t worry about getting them perfectly smooth just yet.
- Add the sour cream and seasonings. Add the sour cream, 2 teaspoons of salt, and 1 teaspoon of black pepper. Gently stir everything together until combined. The potatoes should be thick and creamy, but still soft enough to spread easily. Taste and adjust the seasoning as needed.
- Add the cheddar and green onions. Add 1 cup of freshly shredded sharp cheddar cheese and the sliced green onions, reserving a little green onion for garnish, if desired.
- Mix everything together. Using a large spoon or spatula, gently fold the cheddar and green onions into the mashed potatoes until evenly distributed. Avoid overmixing, which can make the potatoes gummy.
- Transfer to a baking dish. Preheat the oven to 375°F and lightly grease a 9×13-inch baking dish. Spoon the mashed potatoes into the dish, spreading them into an even layer. I like to leave a few swirls and shallow indentations across the top rather than smoothing everything completely flat.
- Add the remaining cheddar. Sprinkle the remaining 1 1/2 cups of shredded sharp cheddar evenly over the top of the casserole. Add a few of the reserved green onions, if desired.
- Bake until hot and melty. Bake for approximately 25 minutes, or until the casserole is heated through and the cheddar has completely melted. Remove from the oven, garnish with additional green onions if desired, and serve warm.
How to Make Mashed Potato Casserole Ahead of Time
If you’re planning to make these baked mashed potatoes ahead of time, the most important adjustment is to double the whole milk from 3/4 cup to 1 1/2 cups total. The extra milk helps keep the potatoes creamy after refrigeration and baking. If the mixture seems a little looser than you normally like your mashed potatoes, don’t worry! The potatoes will thicken as they cool and refrigerate, then firm up a little more as they bake.
- Assemble the casserole. Prepare the mashed potatoes as directed, using 1 1/2 cups of whole milk instead of 3/4 cup. Transfer to your 9×13-inch baking dish and top with the remaining shredded cheddar cheese. Do not bake.
- Refrigerate for up to 2 days. If the potatoes are still hot, allow them to cool slightly, then cover tightly with foil or plastic wrap and refrigerate promptly.
- Remove the casserole from the fridge an hour before baking. This helps take off some of the chill so it heats more evenly in the oven. There’s no need to bring it completely to room temperature.
- Bake. Preheat the oven to 375°F. Tent the casserole loosely with aluminum foil and bake for 25 minutes. Remove the foil and continue baking, uncovered, for another 15-25 minutes, or until the cheese is completely melted and the center reaches 165°F. Plan on approximately 40-50 minutes of baking time altogether.
Storage and Reheating
- Refrigerator: Transfer leftover mashed potato casserole to airtight containers and refrigerate within 2 hours of serving. Leftovers will keep for up to 4 days from when the potatoes were originally cooked. If you made the casserole ahead of time, remember to count those days, too.
- Reheating: The potatoes will thicken in the refrigerator, so I recommend adding a splash of milk to help bring back some of that creaminess. Reheat individual portions in the microwave, stirring occasionally, or cover with foil and warm in a 350°F oven until heated through to 165°F.
- Freezing: I don’t recommend freezing this casserole. With so much sour cream and dairy, the potatoes may become grainy or watery after thawing.
Mashed Potato Casserole FAQs
Absolutely! Just keep in mind that leftover mashed potatoes may already contain butter, milk, and sour cream, so you won’t need to add all the dairy listed in this recipe. Warm the potatoes slightly, adding a splash of milk if needed to make them creamy and easy to spread. Fold in the cheddar and green onions, transfer to your baking dish, and bake until heated through.
Yes! This recipe makes approximately 12 side-dish servings, but you can easily halve the ingredients for a smaller gathering. Use an 8×8-inch or 9×9-inch baking dish instead of a 9×13-inch dish. The smaller casserole may heat through more quickly; start checking it a little earlier.
Nope! Unlike some mashed potato casserole recipes, this one doesn’t need eggs. The potatoes are already cooked before going into the oven, and we’re simply baking them until heated through with a delicious layer of melted cheddar on top. The result is creamy and spoonable rather than firm or sliceable.
Yes! A deep, disposable 9×13-inch aluminum pan is a great option for potlucks and holiday dinners, especially when you’re bringing the casserole to someone else’s house. Place it on a sturdy baking sheet for support when transferring it in and out of the oven. Also keep in mind that baking times may vary slightly depending on the pan.
More Mashed Potato Recipes
If you try this mashed potato casserole recipe, I’d love to hear what you think! Did you make it ahead for a holiday dinner or bake it the same day? Please leave a comment and star rating below letting me know how it turned out. Your feedback is always appreciated and helps other readers, too! Thank you so much! 💛
Mashed Potato Casserole Recipe
Ingredients
- 5 pounds Russet potatoes, peeled and cut into 2-inch pieces
- 2 ½ teaspoons fine sea salt, for boiling the potatoes
- 8 tablespoons (1 stick) butter, cut into pieces
- ¾ cup heavy cream, at room temperature or gently warmed
- ¾ cup whole milk, at room temperature or gently warmed
- ¾ cup EXTRA whole milk, for the make-ahead version only (1 1/2 cups total)
- 16 ounces full-fat sour cream, at room temperature
- 2 teaspoons fine sea salt, plus more to taste
- 1 teaspoon freshly ground black pepper
- 3 green onions, thinly sliced
- 2 ½ cups freshly shredded sharp cheddar cheese, divided (1 cup for the potatoes and 1 1/2 cups for topping)
Instructions
Prepare the Mashed Potatoes
- Prepare and boil the potatoes. Place the peeled and chopped Russet potatoes in a large pot or Dutch oven. Add enough cold water to cover them by approximately 1 inch, then season the water generously with 2½ teaspoons fine sea salt. Bring to a boil over high heat. Reduce the heat to maintain a steady simmer and cook for 15-20 minutes, or until the potatoes are tender enough to break apart easily when pierced with a fork.5 pounds Russet potatoes, 2 ½ teaspoons fine sea salt
- Drain. Pour the potatoes into a large colander and drain thoroughly. Allow them to sit for 2-3 minutes (so excess steam can escape) before transferring them back to the warm pot.
- Mash with butter. Add the 8 tablespoons of butter to the hot potatoes. Using a handheld potato masher, work the butter into the potatoes until melted and incorporated. Continue mashing until most of the larger lumps have disappeared.8 tablespoons (1 stick) butter
- Add the milk, cream, and sour cream. Gradually pour in the 3/4 cup whole milk and 3/4 cup heavy cream, gently mashing between additions. Fold in the 16 ounces of sour cream, 2 teaspoons salt, and 1 teaspoon black pepper. Mix just until combined. The potatoes should be thick and creamy, but soft enough to spread easily. Taste and add more salt if needed.Make-ahead adjustment: If preparing the casserole in advance, use 1 1/2 cups whole milk total instead of 3/4 cup.¾ cup heavy cream, ¾ cup whole milk, 16 ounces full-fat sour cream, 2 teaspoons fine sea salt, 1 teaspoon freshly ground black pepper
- Fold in the cheese and green onions. Add 1 cup of the shredded sharp cheddar and the sliced green onions, reserving a little green onion for garnish if desired. Gently fold everything together with a large spoon or spatula until evenly distributed.3 green onions, 1 cups freshly shredded sharp cheddar cheese
Assemble and Bake
- Prepare the baking dish. Preheat the oven to 375°F. Lightly grease a 9×13-inch baking dish, then spoon in the mashed potato mixture. Spread the potatoes evenly, leaving a few shallow swirls across the surface.
- Add the cheese topping. Sprinkle the remaining 1 1/2 cups of shredded sharp cheddar evenly over the potatoes. If preparing the casserole ahead of time, stop here and follow the make-ahead instructions below.1 ½ cups freshly shredded sharp cheddar cheese
- Bake the casserole. Place the freshly assembled casserole in the preheated oven, uncovered, and bake for approximately 25 minutes, or until the potatoes are hot and the cheese is fully melted. Remove from the oven and garnish with the reserved green onions, if desired.
Make-Ahead Instructions (Optional)
- Add extra milk. When preparing the mashed potatoes in Step 4, increase the whole milk to 1 1/2 cups total. The mixture may look a little softer or looser than usual. That's okay! The potatoes will thicken during refrigeration and baking.¾ cup EXTRA whole milk
- Assemble and refrigerate. Finish mixing the mashed potatoes with the cheddar and green onions, then spread them into the prepared 9×13-inch baking dish and sprinkle with the remaining cheddar. Do not bake. Allow the potatoes to cool slightly, then cover tightly and refrigerate promptly for up to 2 days.
- Remove from the refrigerator. Approximately 1 hour before baking, take the casserole out of the refrigerator to remove some of the chill. Preheat the oven to 375°F.
- Bake covered, then uncovered. Loosely tent the casserole with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for another 15-25 minutes, or until the cheddar is melted and the center reaches 165°F. Total baking time will be approximately 40-50 minutes.
Notes
- Cheese: Freshly shredded sharp cheddar melts more smoothly than most packaged shredded cheese. Use 1 cup in the mashed potatoes and reserve 1 1/2 cups for the topping. Of course, you can always add more cheese if you’d like.
- Leftovers: Refrigerate promptly and use within 4 days of initially cooking the potatoes. Add a splash of milk when reheating, if needed, and heat to 165°F. I don’t recommend freezing this particular casserole because the sour cream and dairy may separate, leaving the potatoes grainy or watery.
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Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
