Mashed Potato Casserole Recipe

Creamy Mashed Potato Casserole made with fluffy Russet potatoes, butter, sour cream, and plenty of sharp cheddar cheese. Baked until hot and melty, it's an easy, crowd-pleasing side dish that can be assembled up to two days ahead of time. Perfect for Thanksgiving, Christmas, and holiday gatherings!

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 9x13-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 9x13-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.

Mashed Potato Casserole Recipe

Ingredients

Instructions

Prepare the Mashed Potatoes

Assemble and Bake

Make-Ahead Instructions (Optional)

Notes

Nutrition