Beat the butter and sugar until frothy. Stir in yogurt and vanilla flavor. Mix the flour with cocoa, drinking chocolate powder and salt, stir in well. Then mix the chocolate chips into the batter. Let the dough cool in the refrigerator for at least 1 hour.
Preheat the oven to 180 ° C top / bottom heat or 160 ° C convection. Cover a baking sheet with baking paper and place the dough spoon by spoon on it, a good 4 cm apart. Bake in the preheated oven for about 8-10 minutes. Leave on the baking sheet for 1 minute, then place on a wire rack to cool.