Preheat the oven to 175°C (approximately 350°F). Beat the butter until fluffy. Gradually mix in the sugar, vanilla sugar, salt, eggs, cocoa powder, flour and baking powder. Mix well.
Line a muffin tin with paper cups and grease wiith the cups with oil. Pour the batter into the muffin tin. Bake for 25-30 minutes. Remove from the oven, let cool and serve.