Method

1. Preheat the oven to 160°C. Line a large baking tray with baking paper. Grease a 7-inch cake ring and place on the prepared tray. Press cookie dough into the cake ring to create an even layer. Bake for 25 minutes until golden, then remove from the oven and cool completely, then remove from the cake ring.
2. To make the buttercream, place butter in a large bowl. Using an electric mixer, beat until pale. Reduce the mixer speed to low and gradually add the icing sugar, beating until well combined. Add the milk and vanilla, increase mixer speed to high, and mix until well combined.
3. Transfer buttercream to a piping bag with a star nozzle. Pipe buttercream around the edge of the cookie cake, then scatter with sprinkles. If you want to write a special message on the cake, place melted chocolate in a piping bag with a very fine nozzle and pipe your message into the centre of the cake.