Whisk the melted butter, sugar, sour cream, milk, eggs and vanilla together in a large bowl.
½ cup (112 g) unsalted butter, melted, 1 cup (200 g) granulated white sugar, ½ cup (122 g) sour cream, at room temperature, ¼ cup (60 ml) whole milk, at room temperature, 2 eggs, at room temperature, 1 teaspoon vanilla
Then add in the mashed bananas and mix to combine.
1 cup (245 g) very ripe bananas, mashed
In a separate bowl, whisk together the flour, baking powder, baking soda and salt. Add the dry ingredients to the banana mixture and combine.
2 cups (250 g) all-purpose flour, spooned and leveled, 2 ½ teaspoon baking powder, ¼ teaspoon baking soda, ½ teaspoon sea salt
Lastly, fold in the mini chocolate chips.
1 cup (200 g) mini semi-sweet chocolate chips
Cover the batter with plastic wrap and let the batter rest at room temperature for 1 hour.
Preheat the oven to 350 degrees.
Line 2 muffin pans with 14 liners, spacing the liners out so each pan has 7 cups lined.
After one hour, scoop the muffin batter into the muffin cups, filling each to the top. Sprinkle extra chocolate chips on top of each.
½ cup (100 g) mini semi-sweet chocolate chips for sprinkling on top of the muffins
Bake the muffins for 22-24 minutes, or until a toothpick comes out clean from the centers.
Let the muffins cool in the pan for 10 minutes, then transer them to a wire rack to finish cooling.