Preheat the oven to 180°C (356°F).
Mix almond flour, cocoa powder, baking powder, and salt together.
In a bowl, cream the room-temperature butter and erythritol until soft and fluffy.
Add the egg and mix well.
Sift the dry mixture in and fold with a spatula.
Add dark chocolate pieces and mix.
Place the dough onto a baking pan, break it up into crumble shapes, and spread it out.
Bake at 180°C (356°F) for 15~20 minutes.
Let it cool and then cut into bite-sized pieces.