Prep the pan and oven: Heat the oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.

Mash the bananas: In a large bowl, mash the ripe bananas until very smooth with minimal lumps. Aim for a puree-like texture for the fudgiest brownies.

Whisk in wet ingredients: Add 1/2 cup creamy peanut butter, 1/3–1/2 cup maple syrup (adjust to sweetness), 2 eggs, and 1 teaspoon vanilla. Whisk until glossy and fully combined. For vegan brownies, use 2 flax eggs (2 tablespoons ground flax + 5 tablespoons water; rest 5 minutes).

Add the dry ingredients: Sift or whisk together 1/2 cup unsweetened cocoa powder, 1/2 cup almond flour or 2/3 cup oat flour, 1 teaspoon baking powder, 1/4 teaspoon fine sea salt, and 1/2 teaspoon espresso powder if using. Fold the dry mix into the wet ingredients just until combined.

Stir in chocolate: Fold in 1/3–1/2 cup dark chocolate chips. The batter will be thick and glossy.

Pan and swirl: Spread the batter evenly in the prepared pan. Warm 2–3 tablespoons peanut butter until runny and drizzle over the top. Use a knife or toothpick to create swirls. Sprinkle with a pinch of flaky salt if you like.

Bake: Bake for 22–28 minutes, until the edges are set and the center looks just slightly underbaked. A toothpick should come out with moist crumbs, not wet batter.

Cool completely: Let the pan cool on a rack for at least 45–60 minutes. For clean slices and maximum fudginess, chill for 30 minutes before cutting.

Slice and serve: Lift out using the parchment and cut into 12–16 squares. Enjoy as-is or with a glass of cold milk or coffee.