Finely cut the chocolate and melt in a bowl au bain marie. Remove from heat when the chocolate is melted. Beat the egg whites until half stiff, add the sugar little by little and stir the mixture until fully stiff. First, mix the egg yolk and cream with the chocolate. Use a spatula. Directly afterwards, carefully combine the egg white to the mixture. Divide the mixture into glasses and place in the fridge.

Right before serving, whisk the cream and water. Whisk until slightly foamy and add the coffee. Pour the cream onto the chocolate mousse and sprinkle a bit of cacao powder. Serve immediately.