Combine cake flour, baking powder, and salt in a bowl.
Cut cold butter and add it to the bowl. Use your hands to mix with the dry ingredients until crumbly.
Add milk, egg, and erythritol, and mix gently.
Chop dark chocolate into small pieces and mix into the dough.
Form the dough into a single ball and let it rest in the refrigerator for 10 minutes.
Roll out the dough to a thickness of 2cm and cut into triangle shapes.
Place on a baking sheet lined with parchment paper and bake in a preheated oven at 180°C for 20 minutes.