Preheat the oven to 200°C (392°F).
Melt the butter and dark chocolate together using a double boiler.
In a bowl, whisk together the eggs and erythritol.
Add almond flour, cocoa powder, and baking powder, and mix well.
Add the melted chocolate mixture and mix until combined.
Pour the batter into muffin molds.
Bake in the oven for 10–12 minutes.