Preheat the oven to 180°C (356°F).
Mash the banana in a bowl.
Add the eggs, unsweetened cocoa powder, almond flour, and baking powder, and mix well.
Melt the dark chocolate using a double boiler or microwave.
Add the melted chocolate to the batter and mix evenly.
Pour the batter into a pan lined with parchment paper.
Bake in the oven for 20 to 25 minutes.
Let cool completely, then cut into desired portions.