METHOD
1. Combine the cake mix, water, vegetable oil, butter and melted chocolate.
2. Pour half the brownie mix into a lined, square tin, then top with Oreos if using. Pour over the rest of the brownie mixture and smooth out.
3. Bake at 170c for 20-25 minutes.
4. Put dark chocolate and double cream into a bowl together and microwave for 1 minute 30 seconds.
5. When the cake has cooked and cooled, pour the chocolate & cream mixture over it and smooth out.
6. Dollop melted white chocolate and use a knife to shape into ghosts.
7. Use the melted milk chocolate to add eyes and mouths.
8. Top with sprinkles, then refridgerate for at least an hour before slicing into 16 pieces.