Melt dark chocolate and unsalted butter together using a double boiler.
Add erythritol and mix well.
Add eggs and whisk thoroughly.
Add almond flour, cocoa powder, and baking powder, and mix evenly.
Line the pan with parchment paper and pour in the batter.
Bake in the oven at 170°C for 20 to 25 minutes.
Let cool completely, then cut into serving sizes.