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1
Combine 55g (1/4 cup) of the caster sugar, hazelnuts and cornflour in a food processor and process until finely ground. Using an electric mixer, whisk egg whites until foamy, add a pinch of salt and whisk until soft peaks form, then gradually add remaining sugar and whisk until mixture is thick and glossy. Carefully fold nut mixture into egg white mixture in 2 batches until just combined. Spoon mixture into a baking paper-lined 1.5cm-deep 26x32cm oven tray, smooth top and bake at 180C for 25 minutes or until golden. Stand meringue in tray for 10 minutes, then turn out onto a wire rack covered with a piece of baking paper and carefully peel off baking paper lining. Cool.
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2
For gianduja filling, process hazelnuts and icing sugar in a food processor until a smooth, oily paste forms (this will take about 5 minutes and you will need to keep scraping down the side of the bowl). Add melted chocolate and process until combined and mixture is smooth. Transfer gianduja to a bowl, stir in one-third of the whipped cream to loosen, then fold in remaining whipped cream until just combined.
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3
For ganache, process chopped chocolate in a food processor until the size of large breadcrumbs. Bring cream just to the boil in a small saucepan. With food processor running, add hot cream to chocolate and process until mixture is smooth. Transfer to a small bowl and cool at room temperature until thick and of spreading consistency.
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4
Cut hazelnut meringue into 4 widthways. Place a meringue rectangle on a serving plate and spread with one-third gianduja filling, then repeat layering twice more, finishing with a layer of meringue. Spread top and sides of cake with ganache and refrigerate until set.
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5
Cake will keep, refrigerated, in an airtight container for up to 1 week.
