Preheat the oven to 180C/350F/gas mark 4
Use an 18 x 28cm/7 x 11 in deep cake tin.
Grease and line the cake tin. Put all the sponge ingredients in a bowl. Mix together and beat until smooth. Pour the batter into the prepared tin. Bake for 25 to 30 minutes until firm to the touch. Turn out, remove paper and cool.
Filling and decoration: Melt the carob chips until runny and keep warm. Whisk the cream with the dissolved coffee and icing sugar until it forms soft peaks. Trim the edges of the cake and cut into three even-sized pieces. Spread a layer of cream on one piece, top with a second layer and spread with more cream. Top with the final layer of sponge cake. Spread the sides with cream. Spoon the carob into a piping bag with a fine nozzle. Pipe straight lines along the length of the cake and draw lines backwards and forwards across the chocolate lines creating a chevron effect. Chill for at least one hour and serve.
