1. Preheat oven to slow 300ºF/150ºC. Line four trays with baking paper. Mark 22cm/9inch circles on three trays and draw straight lines, 3cm/1¼inch apart, on the remaining tray. Place egg whites in large dry mixing bowl. Using electric beaters, beat egg whites until soft peaks form. Gradually add sugar, beating constantly after each addition. Beat 5-10 minutes until thick and glossy and all sugar has dissolved. Gently fold sifted cocoa into meringue mixture.

2. Divide meringue into four portions. Spread three portions onto trays evenly covering marked circles. Place remaining portion in piping bad fitted with a ⅓inch plain piping nozzle.  Pipe long lines over marked lines. Bake meringues for 45 minutes or until pale and crisp. Check meringue strips occasionally to prevent overcooking. Turn off oven, cool meringues in oven with door ajar.

4. Assemble: Place one meringue disc on serving plate, spread with one-third of the mousse mixture. Top with another meringue disc, spread with half remaining mousse mixture. Repeat with remaining meringue disc and chocolate mousse. Run knife around edge of meringue cake to spread mousse evenly over edge. Cut or break meringue strips into 2inch pieces. Pile strips on top of cake and diagonally around outer edge, sticking them to mousse. Dust with extra cocoa. Refrigerate until firm.

3. Filling: Place melted chocolate in bowl, whisk in egg yolks and dissolved coffee and water; beat until smooth. Fold in whipped cream, mix until combined and mixture is firm. Refrigerate until mousse is cold and thick.