Heat the oven to 180 °C. Place paper cups in the cavities of the muffin tray. In a small baking bowl, beat the cream cheese with sugar and vanilla sugar until creamy. In another baking bowl, combine the baking soda, flour, baking powder and cocoa powder. Beat the egg in a large baking bowl and mix lightly. Add the brown sugar, oil, and buttermilk and mix well. Next, gently fold in the flour mixture. Spread 1/4 of the batter evenly in the baking sheet wells. Next, add 1 tsp of filling to each and top with batter. Bake in the oven for 20 to 25 minutes.