Spread across one of the cakes, put the other on top and cover the top and sides. You'll get best results if you use a palette knife to do this.
Decorate with extra Oreos. I cut mine in half with a sharp knife, holding them still with the other hand to minimise cracking.
*If using plain flour add an extra 2 tsp of baking powder and half a tsp of bicarbonate of soda.