For the meringues, whisk the egg whites with the lemon juice until soft peaks form.
Add the caster sugar and continue whisking until stiff, add the icing sugar and ground nuts, then gently fold through until evenly combined. Line a baking tray with baking paper and pipe or spoon out rounds of meringue into 7cm discs.
Bake for 1-2 hrs until crisp outside but still soft in the centre. Leave to cool. You need 3 rounds per person. Leftovers can be kept in an airtight container for about 1 week.
To make the hazelnut praline, warm a small heavy-based pan over a medium heat and cook the caster sugar until it melts and turns a rich caramel colour. Carefully swirl the hazelnuts around the pan (be careful, the sugar is very hot) and allow them to caramelise and brown about 2 mins.
Pour the mixture out onto a tray lined with baking paper. Leave to cool.
Make the chocolate sauce by heating together 75ml water, the caster sugar and cocoa powder until boiling.
Pour over the chocolate and whisk well until smooth.
To serve, whisk the cream until soft peaks form. Finely chop the cooled praline by hand or in a food processor. Stir most of it through the whipped cream, setting a little aside.
Place a meringue disc on each plate and top with a little of the cream.
Add another disc, more cream, followed by the final disc. Top with icing sugar, cocoa powder and some of the reserved chopped praline, then spoon around some chocolate sauce
