Concorde

Preheat the oven to 110 C (225 F) mark 1/4. Lightly brush 2 baking sheets with softened butter and cover with baking parchment. Cut an oval pattern, about 20 cm (8 inches) long and 12.5 cm (5 inchcs) wide, from a thin piece of cardboard. Use the pattern to trace 2 ovals on 1 baking sheet and 1 oval on the second. Leave one-half of the second baking sheet free for piping strips of meringue. Sift together the icing sugar and the cocoa powder. Beat the egg whites with a whisk or electric mixer until soft peaks form. Gradually beat in the caster sugar and then continue beating until stiff peaks form and the meringue is glossy and smooth. Fold in the icing sugar, cocoa and vanilla with a spatula. Fit a piping bag with the large plain tube and fill with the meringue. Pipe the meringue to fill each traced oval, srarting in the centres and working outwards in a spiral. Fit another piping bag with the Medium plain tube and fill with the remaining meringue. Pipe long thin scrips on the second baking sheet, leaving about 2.5 cm (1 inch) in between each. Bake for at least 2 hours, until the meringue is crisp and thoroughly dry. Cool and carefully peel off the paper, then trim the ovals to equal sizes. Bring 5-7.5 cm (2-3 inches) of water to simmering point in a saucepan. Combine the chocolate, butter and 45 ml (3 tbsp) of the sugar in a heatproof bowl and set it over the simmering water Leave to stand, without stirring, until the chocolate has completely melted. Remove from the heat and stir in the egg yolks with a spoon. Heat the egg whites with a whisk or electric mixer until stiff peaks form. Gradually beat in the remaining sugar and continue beating until stiff peaks form and the meringue is glossy and smooth. Whisk about one-third of the egg whites into the chocolate mixture. Gently fold this into the remaining egg whites with a metal spoon. Spread a thin layer of moussse over 1 meringue oval with a palette knife. Place a second oval on top and spread it with a thin layer of mousse. Top with the third meringue and spread the top and sides of the cake with the remaining mousse. Carefully cut the meringue strips into 2.5 cm (1 inch) lengths with a serrated knife and use them to decorate the top and sides of the cake. Sift icing sugar over the top. Cover and refrigerate for 2 hours before serving.