Mash bananas in a mixing bowl. Add egg, vanilla, brown sugar, and granulated sugar and stir well to combine.
In a separate small bowl stir together flour, baking powder, baking soda and salt. Add to banana mixture and stir, just to combine.
Gently stir in melted butter and chocolate chips. Don't over-mix the batter. Let batter rest at least 15 minutes, up to an hour or in the fridge overnight.
Preheat oven to 425 degrees F. Grease muffin pan or use paper liners. Only place muffins in every other hole.
Spoon the batter into prepared muffin pan until it’s ¼” from the top (use ⅓ cup scoop) and bake for 6 minutes at 425, lower temp to 350 and cook 6 - 10 minutes more. Makes 12 muffins.
