01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease with cooking spray.
02 - Whisk mashed bananas, eggs, peanut butter, melted butter, milk, and vanilla extract in a large bowl until smooth.
03 - In a separate bowl, blend together flour, brown sugar, baking powder, baking soda, and salt.
04 - Gently stir dry ingredients into wet mixture until just combined. Avoid overmixing to ensure tenderness.
05 - Fold in chocolate chips or chopped peanuts if desired.
06 - Distribute batter evenly among muffin cups, filling each approximately three-quarters full.
07 - Bake for 18 to 22 minutes or until a toothpick inserted into the center emerges clean.
08 - Allow muffins to rest in the tin for 5 minutes then transfer to a wire rack to cool completely.