Instructions: First make the chocolate cases. Melt the chocolate until smooth in a very slow oven or in a bowl over hot water. Spread the chocolate evenly over the paper cases with the back of a teaspoon. Check that there is no see through patches when you hold them up to the light

( it is a good idea to do a few extra cases to allow for accidents!). Stand each one in a bun tray and leave to form in a cold place. Peel the paper layers off carefully and set aside. Next make the mousse.

Break the chocolate into small pieces and put in a bowl to melt with the butter and water over a low heat. Stir gently until melted and completely smooth. Remove from the heat and leave to cool, then whisk in the rum, if using, and the egg yolks. Whisk the egg whites and fold them in. Beat for 5-6 minutes: this makes the mousse smooth and silky. (Even though it sounds like a contradiction, the mousse thickens as it is beaten at the end). Fill each chocolate case with the mousse. Allow to set for 5-6 hours or overnight.

To serve: Pipe a rosette of softly whipped cream on to each mousse.

Sift a little unsweetened cocoa powder over the top and serve chilled.

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