Preheat the oven to 425℉ and line a 6-hole jumbo muffin tin or a 12-hole normal muffin tin with cupcake liners.
Peel and mash your ripe bananas with a fork, keeping a good amount of chunks.
3-4 medium bananas
Mix together the dry ingredients with a whisk until combined.
1 ½ cups all-purpose flour, 1 teaspoon baking soda, 1½ teaspoons baking powder, ¼ teaspoon kosher salt, ½ teaspoon ground cinnamon
In a separate large bowl, whisk together the sugars, butter, vegetable oil, vanilla, egg, and sour cream until combined. Gently fold in the bananas with a rubber spatula.
½ cup granulated sugar, ¼ cup brown sugar, 6 tablespoons unsalted butter, ¼ cup vegetable oil, 1 teaspoon vanilla paste or extract, 1 large egg, ¼ cup sour cream
Add in the dry ingredients and walnuts and gently fold it into the wet ingredients with a rubber spatula until it is just combined.
½ cup chopped walnuts
Distribute the batter evenly between the liners, filling the whole way to the top, then sprinkle chopped walnuts and the turbinado sugar to cover the tops.
demerara or turbinado sugar for muffin tops
Bake at 425℉ for 5 minutes, then reduce the temperature to 400℉.
For jumbo muffins, bake for an additional 15-18 minutes. For regular muffins, bake for an additional 11-14 minutes. For either, you want a toothpick inserted in the center to come out clean with no wet batter.