Combine oat flour, almond flour, and cocoa powder in a bowl.
Add erythritol, baking powder, and salt.
Add eggs, milk, and unsweetened yogurt, then mix into a batter.
Stir in chopped dark chocolate into the batter.
Pour the batter into a mold and spread evenly.
Bake in a preheated oven at 180°C for 20 minutes.
Let it cool and cut into portions.