Preheat the oven to 350 F (177 C). Line an 8x8 pan with parchment paper along the bottom and two sides.
Mash 2 medium bananas until mostly smooth with very few lumps. Measure out the mashed banana in a measuring cup.
⅔ cup mashed banana
Add the unsalted butter and semi sweet chocolate chips to a heat safe bowl. Heat the butter and chocolate until fully melted and well combined. This can be done as a “bain marie” or in the microwave. If using the microwave, heat the mixture 30 seconds at a time, stirring between heating intervals until fully melted and combined.
½ cup (113 g) unsalted butter, ½ cup (3 oz., 85 g) semi sweet chocolate chips
Gently stir in the granulated sugar just to barely combine and return the mixing bowl to the microwave. Heat for 30 more seconds. Now stir the sugar fully into the melted butter and chocolate. Allow the mixture to sit for 5 minutes if needed to cool to warm, rather than hot.
1 cup (200 g) granulated sugar
Stir in the eggs, mashed bananas, vanilla extract, cocoa powder and salt until smooth and glossy. This takes many whisks around the bowl. Lift the flexible spatula or spoon and allow the batter to drizzle down. If the batter falls like a ribbon, it’s perfect. Stir in the flour until well combined. Fold in the additional chocolate chips. 2 large eggs, room temperature, 1 teaspoon vanilla extract , ¼ teaspoon salt , ⅓ cup (30 g) Dutch processed or unsweetened cocoa powder, ¼ teaspoon baking powder, ½ cup (60 g) all purpose flour , ½ cup (3 oz. 85 g) chocolate chips or chunks
Evenly pour the brownies with mashed banana into the prepared pan. Bake for about 30 - 40 minutes. The brownies are ready when a toothpick inserted into the center comes out with a few moist crumbs. Start checking at 30 minutes. If the toothpick comes out with wet streaks, the brownies will need another 5 - 10 minutes.
Cool the brownies in the pan for at least one hour at room temperature. Then transfer the brownies into the fridge for another hour to fully set.
When it’s time to serve, remove the brownies from the pan using the parchment paper overhang. Slice the brownies, serve with more sliced bananas, whipped cream or enjoy as is.