Mix the cream cheese with the vanilla sugar. In a second bowl, whisk the egg, stir in sugar, oil and buttermilk. Sift flour with baking powder, baking soda and cocoa powder and fold in. Preheat oven to 180 degrees.
Grease the hollows of the muffin tin. Pour 1/4 of the dough into the wells and pour 1 teaspoon of cream cheese cream on each. Cover with the rest of the batter.
Bake muffins for 20-25 minutes. Let cool, remove from the mold. Melt the glaze in a hot water bath. Dip muffins and place on a rack. Sprinkle on the crumble and let it dry.