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

Mash the bananas. In a large bowl, mash the ripe bananas until mostly smooth with a few small lumps. Aim for about 3/4 to 1 cup of mashed banana.

Whisk in wet ingredients. Add melted butter, granulated sugar, brown sugar, eggs, and vanilla. Whisk until glossy and well combined, about 30–45 seconds.

Sift the dry ingredients. Over the bowl, sift flour, cocoa powder, salt, and baking powder. This helps prevent cocoa clumps and keeps the brownies tender.

Fold gently. Switch to a spatula and fold the dry ingredients into the wet just until no dry streaks remain. Do not overmix or the brownies can turn cakey.

Add chocolate. Fold in the chocolate chips or chunks, reserving a small handful for the top. If using nuts, fold them in now.

Spread and top. Scrape the batter into the prepared pan and smooth the surface. Sprinkle the reserved chocolate on top. Add a pinch of flaky sea salt if you like contrast.

Bake. Bake for 24–30 minutes, rotating the pan once. The edges should be set, and a toothpick inserted 2 inches from the edge comes out with moist crumbs (not wet batter).

Cool for clean slices. Let the pan cool on a rack for at least 30–45 minutes. For the fudgiest texture, chill for 20 minutes before slicing.

Serve. Lift out using the parchment and cut into 9–16 squares. Enjoy as is or warm slightly and top with ice cream.