Place 5 egg whites in the bowl of an electric mixer and whisk until stiff peaks almost form. Gradually add 120g caster sugar until incorporated well. Turn off the mixer.
Combine well the cocoa with 150 grams of icing sugar, then gently fold in. Transfer preparation to a piping bag fitted with a round 1 cm nozzle and pipe two disks about 18 cm in diameter onto a tray lined with baking paper. Also pipe 4 or 5 long, thin sticks of meringue.
Bake meringue in oven for about 1 hour at 90 °C. After that time, turn oven off and leave meringue in the oven for an extra 30 minutes.
Place chocolate in a bowl with the butter and whisky and place over a bath of warm water.
Stir chocolate and butter until smooth and well mixed. Remove bowl from over the water bath.
Beat 4 egg whites into stiff peaks, then slowly add 100 grams of caster sugar until well incorporated. Fold a little of the beaten egg whites into the melted chocolate, then fold in remaining egg whites until just mixed.
Spoon chocolate mousse into piping bag.
Chocolate sponge cake
Grease 2 deep, 20 cm round cake tins, lined with baking paper.
Sift the 3 flours, cocoa and pinch of salt 3 times to aerate.
Preheat the oven to 180°C.
Using an electric mixer, beat eggs and sugar in a large bowl on medium-high speed for 6 minutes, or until mixture is thick, pale and has tripled in volume. Gradually sift the flours over the egg mixture while at the same time folding in with a large metal spoon until just combined.
Divide mixture between prepared tins. To level the batter, gently spin the tins on kitchen counter. Bake for 20 mins. or until the cake has shrunk slightly from the sides and springs back when touched gently. Turn out onto wire cooling rack that has been lined with baking paper.
Carefully peel the baking paper from the base and then leave to cool. Bring the cream and milk to the boil. Remove from the heat and add the chocolate whilst stirring with a wooden spoon, until the chocolate has melted. Once the chocolate has melted the sauce can be served hot or set aside to use cool.
Start with a thin base of sponge cake and build up 3 layers of mousse then meringue layers. Finish with a final layer of mousse on top. Break the thin meringue sticks into 2 cm pieces and cover the sides and top of the cake with them. Dust with a little icing sugar and cocoa powder mixed together.