Finely chop the dark chocolate.
Melt the unsalted butter and dark chocolate using a double boiler or microwave.
Add eggs and erythritol to a bowl and whisk thoroughly until foamy.
Mix the melted chocolate and butter into the egg mixture.
Sift in the almond flour, cocoa powder, and salt, then gently fold together.
Pour the batter into muffin cups or small tart molds.
Bake in a preheated oven at 180°C (356°F) for 10–13 minutes.
Let cool completely, then remove from molds and serve on a plate.