Mix caster sugar, stork, flour, cocoa powder and eggs together in a large mixing bowl.
Line a cupcake tin with paper cases and add one whole Oreo to the bottom of each case. Spoon in cupcake mixture until around 2/3 full.
Put into oven and cook on 180 degrees fan for 25 minutes
During cooking prepare icing. Whip butter for 5 mins. Add icing sugar as usual.in two separate goes stirring thoroughly between each. Add a packet of Oreos to food processor and 'blend' into small pieces. Stir in these Oreo pieces into the icing and fill piping bag ready for icing.
After cooling, Ice the cupcakes with Oreo-Vanilla icing and then add a whole Oreo to the top of each cupcake within the icing