This popular bistro dessert can be made up to two days in advance - indeed, it improves if left to mature before serving. Although chocolate mousse can be made plain, in France it is often flavoured with candied orange peel, ginger, or coffee. Orange-flavoured brandy, rum and cognac are other additions used in small doses to complement the chocolate taste. This recipe adds hazelnuts and whisky to the basic mousse mixture, producing an excellent result.
NOTE: Although the mousse may be prepared well in advance, the Chantilly cream decoration should not be made and applied more than an hour before serving.
60 g (2 oz) skinned hazelnuts, crushed
450 g (1 lb) plain chocolate, cut into small pieces
30 g (1 oz) butter
200 g (7 oz) sugar
6 egg yolks
85 ml (3 fl oz) whisky
6 egg whites
225 ml (8 fl oz) double cream
Few drops vanilla essence
30 ml (2 tbsp) icing sugar
EQUIPMENT: Piping bag, large star icing tube
Prepare the mousse: preheat the oven to 200 C (400 F) mark 6. Spread the crushed hazelnuts on a baking sheet and toast until fragrant and golden brown. Bring about 2.5 cm (1 inch) of water just to simmering point in a saucepan. Combine the chocolate, butter and half the sugar in a heatproof bowl and set the bowl over the simmering water. (The water must not touch the bottom of the bowl.)
Leave to stand without stirring until the chocolate has melted. (If you stir the chocolate it may stiffen or "seize" and become unworkable.) Remove the bowl from the heat and stir in the egg yolks. Stir in the hazelnuts and whisky.
Beat the egg whites with a whisk or electric mixer until stiff peaks form. Gradually beat in the remaining sugar and continue beating until the mixture is stiff and shiny. Whisk about one-third of the egg whites into the chocolate mixture (it is fine to whisk vigorously this step serves to lighten the chocolate mixture sufficiently that it may be folded into the remaining whites without diminishing their volume). Gently fold the chocolate mixture into the remaining whites with a metal spoon. Pour the mousse into a serving bowl or individual dessert glasses. Refrigerate for 2-3 hours until firm.
Chill a mixing bowl for the Chantilly cream.
Not more than 1 hour before serving, prepare the Chantilly cream: combine the cream and vanilla in the chilled bowl and beat with a whisk or electric beater until the cream begins to stiffen. Add the icing sugar and continue beating until stiff peaks form and the cream clings to the whisk or beater. Fit the piping bag with the star tube and fill with the Chantilly cream. Refrigerate until ready to serve. To serve, pipe rosettes of Chantilly cream on top of the mousse(s) and serve any remaining cream in a sauceboat.