For hazelnut meringues, preheat oven to 130C. Whisk eggwhites in an electric mixer until soft peaks form. With motor running, add white sugar in batches, allowing each addition to incorporate before adding the next, until all is incorporated. Sift over icing sugar and fold through nut meals until just combined. Spread mixture into sixteen
7.5cm-diameter circles on baking paper-lined oven trays and bake, rotating trays once, until meringues are dry (1-1½ hours). Turn off oven and leave to cool completely.
Meanwhile, whisk egg yolks and sugar in an electric mixer until thick and pale. In a separate bowl, whisk cream until soft peaks form and refrigerate until required. In another bowl, whisk eggwhites and a pinch of salt until firm peaks form. Fold egg yolk and eggwhite mixtures, cream, chocolate and hazelnuts together and set aside.
Trim meringues with a 7.5cm-diameter cutter and place half the meringues in eight 7.5cm-diameter deep-ring moulds placed on a baking paper-lined oven tray (see note). Divide chocolate mixture among moulds, top with remaining meringues and freeze until firm (6 hours or overnight). Remove from moulds, dust with cocoa and serve immediately.
Note If you don’t have moulds, you can improvise by cutting stiff cardboard into eight 30cm x 7cm strips, and joining the ends with sticky tape to form rings.