Heat oven to 350°F (177°C). Line muffin cups with paper liners. This recipe makes 12 regular-sized muffins.
Whisk the flour, baking powder, baking soda, and salt in a large bowl.
In another bowl, whisk the mashed banana, melted butter, brown sugar, egg, and vanilla until blended.
Stir the banana mixture into the dry ingredients until you no longer see streaks of flour.
Stir in the chocolate chips.
Fill muffin cups ¾ full. Bake until a toothpick can be inserted and comes out clean, 20 to 25 minutes. Cool on a wire rack.
