Preheat an oven to 180c (350f) and prep a parchment paper-lined 8 by 8 baking pan.
In a large mixing bowl, add the butter and the dark chocolate. Melt completely in the microwave or on a Bain Marie.
Into a large mixing bowl, add the eggs, and sugar, and use a whisk to whisk the egg and sugar for 3 minutes until the mixture becomes pale and thick.
Transfer the melted chocolate and butter mixture to the egg mixture and sift the cocoa powder. Add the vanilla extract, banana puree, salt, and espresso powder.
Sift the flour and fold the mixture with a rubber spatula until the batter is almost combined.
Pour the batter into a parchment paper lined 8 by 8 brownie pan and smooth it out with an offset spatula. Bake in a 180c (350f) preheated oven for 30-35 minutes. Do not overbake it to keep it fudgy!
Allow the brownies to cool for at least 30 minutes before slicing, so they won't crumble and fall apart. I recommend topping every slice of brownie with a slice of banana.
Notes
Use room temperature ingredients. It is important that you use room-temperature ingredients like eggs. This step ensures that your mixture mixes into a homogenous mixture and bakes perfectly. you don’t want to place cold batter into the oven.
Don’t overmix the batter. For a fudgy texture, avoid overmixing your brownie batter once you add flour. Mix just until combined to keep from incorporating too much air.
Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.
Monitor baking time. Keep an eye on your brownies as they bake. overbaking can lead to dry brownies instead of that desired fudgy consistency. A toothpick inserted should come out with a few moist crumbs.
Spread the batter evenly. Use a spatula to spread the batter evenly in the pan. This ensures uniform cooking and prevents some parts from being overcooked while others remain undercooked.
Use only ripe bananas for this recipe! ripe bananas are more sweet, moist, and easy to mash into a pudding consistency. If you don't have ripe bananas, bake regular bananas in a 200c (400f) preheated oven for 10 minutes, this will soften the bananas and make them into a ripe banana texture.
Cool completely before slicing. Allow your brownies to cool completely before slicing into the brownies to ensure you have clean slices.
Line your baking pan with parchment paper to prevent the brownies from sticking to the pan.