Coarsely chop 4 biscuits. Line the hollows of a muffin tray (for 12 pieces) with paper cups and place 1 biscuit in each. Cream fat, sugar, vanilla sugar and 1 pinch of salt with the whisk of the hand mixer.
Stir in the egg. Mix flour and baking powder and stir in briefly, alternating with the buttermilk. Fold the roughly chopped biscuits into the dough.
Spread the dough into the moulds. Bake in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) for approx. 25 minutes. Let them cool down.
Coarsely chop 4 biscuits. Decorate the Oreo muffins with 1 teaspoon of sour cream and the chopped biscuits.