01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or grease lightly with cooking spray.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt until evenly distributed.
03 - In a large bowl, mash ripe bananas thoroughly. Add peanut butter, brown sugar, oil, eggs, and vanilla extract. Beat until smooth and well blended.
04 - Pour milk into the wet mixture and stir until fully incorporated.
05 - Add dry ingredients to wet ingredients all at once. Fold gently with a spatula just until flour disappears—small lumps are fine. Over-mixing will create tough muffins.
06 - Gently fold in chocolate chips or chopped peanuts if desired.
07 - Divide batter evenly among prepared muffin cups, filling each about 3/4 full.
08 - Bake for 18-22 minutes until tops are golden and a toothpick inserted into the center comes out clean or with just a few moist crumbs.
09 - Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.