Preheat oven to 350°F

In a medium mixing bowl, mash banana and add brown sugar, vanilla and egg

Stir to combine

Add flour, cocoa powder, baking powder and stir until just combined

Stir in milk

Measure out peanut butter into a microwave safe bowl and microwave for 15 seconds to soften peanut butter until it is easy to pour

In a 9×9 baking dish, spray with non stick spray and pour brownie batter into pan

Pour peanut butter on top and take a knife over the top and swirl the peanut butter into the brownie batter

Bake for 25 minutes or until knife or toothpick inserted into the center comes out clean

Allow to cool for 10 minutes before cutting