Prepare the pans: For standard muffins, preheat the oven to 375°F and line two standard muffin tin with 18 paper liners.For jumbo muffins, preheat the oven to 425°F and line two 6-cup jumbo muffin pans with 12 paper liners. Alternatively, bake the jumbo muffins in two batches. Combine the dry ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
3¾ cups all-purpose flour, 1 tbsp + 2 tsp baking powder, 1½ teaspoons baking soda, 1½ teaspoons ground cinnamon, ¾ teaspoon salt
Mash the bananas: Add the bananas to the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until mashed. A large mixing bowl and handheld mixer may also be used.
4 large bananas
Mix the wet ingredients: Add the vegetable oil, granulated sugar, and brown sugar to the mashed bananas. Mix for 1-2 minutes, or until well combined. Add the eggs one at a time, mixing after each addition. Mix in the vanilla extract and milk.
½ cup vegetable oil, ¾ cup white sugar, ½ cup light brown sugar, 3 large eggs, 1¼ cups milk, 3 teaspoons vanilla extract
Make the batter: Add the dry ingredients to the wet ingredients. Mix on low speed just until combined. Do not overmix. Fold in the chopped walnuts or pecans with a rubber spatula.
1½ cups crushed walnuts or pecans
Fill the muffin pans: Divide the batter evenly among the prepared muffin liners. Sprinkle the tops with additional chopped walnuts or pecans, if desired.
Bake standard muffins: Bake standard muffins at 375°F for 16-20 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Bake jumbo muffins: Bake jumbo muffins at 425°F for 5 minutes. Without opening the oven door, reduce the temperature to 375°F and continue baking for 20-25 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Cool: Allow the muffins to cool in the pans for 5-10 minutes. Transfer them to a wire rack to cool completely.