Combine oatmeal and cake flour in a bowl.
Add baking powder, salt, and stevia.
Cut cold butter into small pieces and mix in by hand.
Add egg and milk, then knead the dough.
Gently fold in dark chocolate pieces.
Shape the dough into rounds on a pan.
Bake in a preheated oven at 180°C for 20 minutes.
Cool on a wire rack.