Preheat oven to 350 degrees.

Spray a 9x9 baking pan with non stick cooking spray. Line with parchment paper as well.

In a mixing bowl, combine mashed bananas, melted butter, sugar, and vanilla.

To the banana mixture add flour, salt, and cocoa powder. Stir until completely combined.

Pour batter into baking dish.

Dot the top of the batter with spoonfuls of peanut butter. Use a spatula or butter knife to swirl peanut butter completely into batter.

Bake for 25-30 mins or until set in the middle.

Allow brownies to cool before serving. Use the parchment paper to lift brownies out of pan before cutting.

Sprinkle with powdered sugar if desired.