Pre-heat oven to 190°C/375°F/Gas Mark 5. Place the chocolate sponge mix in a bowl fitted with whisk beaters. Blend in the water on slow speed for 1 minute, scrape down and mix on medium for 5 minutes. Pour into a shallow greased tin 25cm x 35cm (10" x 14") and bake for approximately 35 minutes.
Once cooled, cut the sponge into fingers and place in the bottom of a sundae glass.
Spoon the raspberry compote on top of the sponge.
Pipe or spoon the custard, layering it on top of the compote.
Spoon a ball of vanilla ice cream on top of the custard then repeat the process.
Pipe the whipped cream onto the ice cream and top with a glacé cherry.