For the coffee muffins, preheat the oven to 160 °C, grease the muffin tins as needed. Beat the eggs with sugar and liqueur until foamy. Stir in the coffee yogurt and cocoa powder.
Slowly add the oil. Mix flour with baking powder and fold in alternately with milk (milk as needed, the batter should be slightly thicker).
Pour the batter into muffin cups and bake at 160 °C hot air for about 15-20 minutes.