Mix almond flour, coconut flour, baking powder, and salt evenly in a bowl.
In a separate bowl, whisk together eggs, erythritol, and butter until creamy.
Combine both mixtures and mix well.
Fold in chopped dark chocolate or nuts.
Divide the dough into 6 to 8 equal pieces and shape them into rounds.
Line a baking tray with parchment paper and place the dough pieces on it.
Bake in a preheated oven at 180°C (356°F) for 20–25 minutes.
Let cool before serving.