Have ready a 20 cm square tin, fully lined with greaseproof paper.

For the base: Put the OREO Cookie Pieces into a food processor and blitz to a fine crumb. Add the melted butter and whizz until thoroughly mixed. Press the mixture, very firmly into the base of the lined tin. Chill until the caramel is ready.

For the caramel: Gently heat the sugar and butter in a heavy based, non-stick pan, stirring until melted. Add the condensed milk and bring to a rapid boil, stirring continuously. Cook for about 2 minutes or until the caramel has thickened. Pour the caramel over the OREO base. Allow to cool and set.

For the chocolate topping: Melt the Bournville in a bowl over a saucepan of simmering water. Meanwhile pop the white chocolate into a disposable piping bag and melt in the microwave on a low setting.

Pour the melted dark chocolate over the set caramel and spoon to cover the surface completely. Immediately pipe thin lines of white chocolate over the dark chocolate and create a feather pattern using a knife tip. Chill until the chocolate has set. Remove from the tin before cutting into small portions, using a sharp knife which has been dipped in hot water.