Preheat the oven to 180°C (356°F).
Mix butter, brown sugar, and sugar until creamy.
Add egg and vanilla extract, and blend well.
Sift flour, cocoa powder, baking powder, and salt. Add to the mixture and mix evenly.
Add dark chocolate and milk chocolate, then combine thoroughly into the dough.
Take an appropriate amount of dough, shape into a ball, and place on a baking sheet.
Bake in the preheated oven for 14-16 minutes.
Let cool completely before eating.