Prepare: Preheat oven to 425ºF. For standard-size muffins, line two 12-cup muffin tins with silicone cupcake liners or paper cupcake liners or spray with nonstick cooking spray. For jumbo muffins, line two 6-cup jumbo muffin tins with silicone cupcake liners or paper cupcake liners or spray with nonstick cooking spray. Set aside In a large mixing bowl, whisk together flour, baking powder, salt and cinnamon. Set aside.
2 ½ cups all-purpose flour, 1 tablespoon baking powder, 1 teaspoon kosher salt, 1 teaspoon cinnamon
In a separate large bowl, mix together with a wooden spoon the vegetable oil, brown sugar, eggs, milk and sour cream until well incorporated.
⅓ cup vegetable oil, 1 cup dark brown sugar, 2 large eggs, ½ cup whole milk, ½ cup full-fat sour cream
Add in the mashed banana until well combined.
1 cup mashed overripe bananas
Gently fold in the dry ingredient mixture until no dry spots of flour are left.
Gently fold in chocolate chips.
1 ½ cups semi-sweet chocolate chips
Fill each cup of muffin tin almost to the top with muffin batter. For jumbo muffins, this will make about 8 muffins. For standard-size muffins, this will make about 16 muffins.
Bake for 5 minutes at 425ºF, then lower the oven temperature down to 350ºF for another 22-24 minutes for jumbo muffins or 15 minutes for standard-size muffins, or until a toothpick inserted into the center of the center muffin comes out clean. Allow to cool in muffin tins for 10 minutes, then transfer to a wire rack to cool completely.