Preheat oven to 180c.
Grease 3 x 7" round sandwich tins and line the bottom with baking paper.
Cream your room temperature butter with your sugar until it’s pale, light and fluffy.
Beat in the eggs, one at a time, wiping down the sides of the bowl as you go and ensuring everything is well mixed. (It might start to look a little curdled, don't worry!)
After this, mix in your flour and cocoa. If you’ve been using a mixer, do this bit by hand. It helps to keep the sponge light.
Stir in the melted and slightly cooled chocolate.
Spoon into your tins, smooth out with the back of a spoon. Make a bit of a dip in the middle to account for rising
Bake for about 30 minutes or until a skewer comes out clean. You might need to adjust the time by 5 minutes either way depending on your oven.
Meanwhile make your icing. Beat your butter until it’s pale, light and fluffy.
Use a food processor to blizz one pack of your Oreos to a fine dust.
Beat in your icing sugar, once you are happy with the consistency fold in the crumbled Oreos.
When your cakes are completely cold, use a carving knife to level them. Just trim the top crust off. Remember, this is important, it’s not a waste of cake. If you don’t do this, with a cake this size it will be wonky.
Top each layer with a spread of your oreo buttercream.
Pipe a circle around the outside of two of the layers, sit each on the one before.
On the top layer, pipe small dollops all over, and top with your whole Oreo biscuits.
Enjoy!