01 -
Preheat the oven to 350°F (180°C) and grease and line an 8x8-inch (20x20cm) baking pan with parchment paper. Set aside.
02 -
In a medium mixing bowl, combine the flour, baking powder, and salt.
03 -
In a separate mixing bowl, whisk together the melted butter, granulated sugar, eggs, and vanilla extract.
04 -
Gradually mix the wet ingredients into the dry ingredients until well combined. Divide the batter evenly into two separate bowls.
05 -
In one bowl, sift in the unsweetened cocoa powder and stir in the chopped bittersweet chocolate.
06 -
In the other bowl, stir in the mashed bananas until fully incorporated.
07 -
Dollop the chocolate brownie batter into the prepared pan, then pour the banana batter on top. Swirl the chocolate batter through the banana batter using a butter knife, creating a marbled effect without fully mixing.
08 -
Bake in the preheated oven for 40-45 minutes, or until a wooden skewer inserted in the center comes out clean. Let the brownies cool completely before cutting into squares.
09 -
Store the brownies in an airtight container at room temperature for up to 3 days, or freeze for up to 2 months. Defrost at room temperature or heat in the microwave for 1 minute before serving.