Melt the butter. Mix vanilla sugar, sugar, cocoa, baking powder, flour, and salt well together. Stir butter and milk into the flour mixture. Fold chocolate chips into the mixture. Grease the cups with a little butter. Divide the batter between the two cups. Bake the mugcakes together in the microwave for 2 - 2 1/2 minutes. Serve with a bit of ice cream or whipped cream.