Instructions: Preheat the oven to 200C/gas 6.

Whisk eggs and sugar together until the mixture is light and fluffy.

Trail some of the mixture on top of the rest - when it leaves a thick trail behind, its ready. Fold the cocoa and cornflour mixture in, taking care not to break down the volume. Pour into a greased and lined roulade tin and bake for 7-8 minutes until the mixture is firm and springy. Turn out and cool.

Cut into 2 circles to fit the bottom of a deep cake tin. Use one and freeze the other for next time.

Make a rum syrup by dissolving the sugar in the rum and water. Bring to the boil and simmer until a heavy syrup is produced. Brush the sponge base with the syrup, then set aside.

To make the truffle, grate the chocolate and stand the cream in a warm place. Melt the chocolate very gently in a double boiler. Dont allow the water to boil as this will make the chocolate grainy.

Whisk the cream to a light floppy consistency. Fold it into the chocolate gradually, using a balloon whisk. Pour into the cake tin over the prepared sponge. Smooth the top and leave in the fridge to set, which will take 4-5 hours.

Dust the cake thickly with cocoa or cover with a thin layer of melted chocolate.

To make the chocolate rum sauce, melt the butter, chocolate and cream together in a double boiler. Add the rum and gradually beat in the icing sugar. Add more rum to taste. The sauce should be dark and glossy. Serve with the sponge.

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