Preheat the oven to 375 degrees Fahrenheit and spray a muffin liner with pan spray and, if desired, line it with muffin liners.
Add 1 cup overripe bananas,1 large egg,¼ cup sour cream, 1 ½ teaspoons vanilla extract, ¼ cup unsalted butter,2 tablespoons vegetable oil, ¼ cup brown sugar,and ½ cup granulated sugar to a large bowl and beat with a hand mixer until combined.
Add 1 ⅔ cup all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, and ½ teaspoon salt to a medium bowl and whisk until combined. Add the dry ingredients to the wet ingredients and mix until just combined.
Fold in 1 cup milk chocolate chips by hand. Scoop the batter into the prepared muffin pan until each muffin well is ⅔ of the way full.
Bake for 18-22 minutes or until a toothpick comes out clean from the center of a muffin. Let the muffins cool for 5-10 minutes before serving.