In the bowl of a stand mixer, beat butter, peanut butter, sugar, and eggs.
In a separate bowl, stir together flour, baking powder, baking soda, and salt.
While the mixer is on low speed, alternate adding the flour mixture and the milk until all is incorporated. Add in the bananas and stir until mixed well.
Divide batter evenly among 18 muffin cups lined with paper liners. Bake at 400 degrees for 18 - 20 minutes or until a tester comes out clean. Allow muffins to cool completely before serving. Store in a zip top bag or freeze for later use.