Preheat oven to 350°F (180°C). Line an 8-inch square pan with lightly oiled parchment paper. Set aside.

Peel the ripe bananas and weigh the amount for precision. It matters because too many bananas make the brownies too moist, and on the other hand, the brownies are too dry with fewer bananas.

Roughly cut bananas in pieces in place the bowl of a food processor along with the natural peanut butter. Add vanilla extract and sweetener now if desired.

Process until creamy and smooth, then add cocoa powder and keep blending until fully incorporated.

You may have to stop the food processor a few times and scrape down the sides of the bowl. Blend for extra 20 seconds after that to bring all ingredients together. The batter should be thick and smooth.

Bake for 20-30 minutes, check after 20 minutes, inserting a toothpick in the center of the brownies. If it comes out clean, it's ready. If sticky, keep baking, checking every 5 minutes.

When dry on top and crackle, it's cooked through.

Cool down on a wire rack for 30 minutes before slicing into 16 squares.

Serve plain or with an extra drizzle of peanut butter on top.