|Prep time: 10 minutes||Cooking time: 25 minutes||Total time: 35 minutes|
Heat oven to 350 degrees F. Line muffin cups with paper liners.
Whisk the flour, brown sugar, baking powder, baking soda, and salt in a large bowl. In another bowl, whisk the melted butter, mashed banana, egg, and vanilla until blended. Add the banana mixture to the bowl with dry ingredients then use a fork to combine. Do not over mix. Stir in chocolate.
Fill muffin cups 3/4 full. Bake until a toothpick can be inserted and come out clean, about 25 minutes.