Heat the oven to 180C/160C fan/gas 4. For the meringue, tip all the nuts onto a baking tray and roast for 10-12 mins, shaking the tray halfway through cooking, until toasted. Leave to cool completely. Reduce the oven to 150C/130C fan/gas 2.

Line three baking sheets with baking parchment. Use the base of a 20cm cake tin as a template to draw a circle on each sheet of parchment, then flip these over on their trays to prevent the pen from marking the meringue. Tip the cooled nuts into a food processor and whizz to a powder. Blitz in the icing sugar and cornflour, and set aside.

Tip the egg whites into a large, clean bowl (any oil in the bowl will prevent the egg whites from whipping up fully). Add a pinch of salt and whisk with an electric whisk or in a stand mixer for 3-5 mins until fluffy and doubled in volume. Add the caster sugar, a spoonful at a time, whisking continuously until all the sugar has been incorporated and the meringue is glossy and stiff. Scatter the ground nut mixture over the surface, then use a large metal spoon to gently fold this into the meringue. Transfer the meringue to a piping bag fitted with a large round nozzle.

Starting in the centre of one of the circle templates, pipe a tight spiral of meringue to the edge so the circle is filled. Repeat with the remaining two templates, then use up any leftover meringue to fill any gaps. Smooth the surfaces of the meringue discs with a palette knife so they're flat on top. Bake the meringues for 1 hr, swapping the trays around after 30 mins so they cook evenly. After 1 hr, leave to cool in the oven with the door closed for at least 2 hrs, or overnight.

To make the coffee diplomat, warm the milk, the 300ml cream and coffee in a pan over a low heat until just steaming (don't let it boil). Meanwhile, briefly whisk the vanilla, cornflour, caster sugar and egg yolks together in a large bowl until just combined. Slowly pour the hot milk mixture over the egg yolk mixture, whisking continuously. Strain the mixture through a sieve back into the saucepan, then set over a low-medium heat and cook, stirring continuously with a rubber spatula to prevent the mixture from burning, for 4-5 mins. Don’t rush this as the eggs can easily scramble. After this time, the custard should be thick and smooth. Remove the pan from the heat, scrape the custard into a clean bowl, cover the surface and chill for 1-2 hrs until completely cold.

For the praline, toast the hazelnuts in the oven as you did the nuts in step 1. Lightly oil a baking tray. Weigh the sugar out into a pan and set over a medium heat. Cook, without stirring, until the sugar has dissolved and turned from amber to deep caramel – you can swirl the pan occasionally, but don't stir. Tip in the toasted hazelnuts and swirl to coat in caramel, then tip onto the oiled baking tray. Sprinkle over a pinch of salt and leave to set until hard, about 20 mins. Once set, break the praline into shards and blitz in a food processor to a coarse rubble.

To make the ganache, put the chocolate and a pinch of salt in a heatproof bowl. Warm the cream in a saucepan over a low heat until just steaming, then pour this over the chocolate. Leave to stand for 3-4 mins until the chocolate has melted, then stir into a thick, glossy ganache. Leave to cool at room temperature until needed.

When the coffee diplomat has cooled and set, beat it with a spatula to loosen slightly, then fold in the 100ml lightly whipped cream, a spoonful at a time, until fully incorporated. Spoon into a piping bag fitted with a round nozzle.

Put one meringue disc on a plate, sticking it down with a small blob of the coffee diplomat. Spread half the ganache over the meringue, then pipe over a third of the diplomat. Repeat once, then top with the final meringue and pipe the rest of the diplomat on top. Scatter over the praline rubble, then decorate with gold leaf or lustre, if you like. Best eaten straightaway, but will keep chilled for up to three days.