Hazelnut meringue cake

Method

1. For the meringue, heat the oven to 180°C/fan160°C/gas 4. Draw an 18cm circle on each of 4 sheets of baking paper, then use to line 4 lightly oiled baking sheets.
2. Grind the nuts in a food processor with 1 tbsp of the caster sugar until finely ground with some texture – don’t overgrind or it will become oily. (If you prefer, you can use a pestle and mortar or finely chop the nuts with a knife, then mix with the sugar.)
3. Put the egg whites in a spotlessly clean mixing bowl and whisk with an electric hand mixer to stiff peaks (they shouldn’t droop when the beaters are removed). Add the remaining caster sugar to the whites a tablespoon at a time, whisking back to stiff peaks each time. Once you’ve added half the sugar, start adding in larger quantities, whisking back to stiff peaks each time. Once all the sugar has been added, whisk in the vinegar to form stiff peaks, then fold through the hazelnuts with a metal spoon or balloon whisk.
4. Spoon or pipe the meringues in circles onto the baking paper to give 3 flat circles and the fourth circle swirled a bit thicker (this will form the top layer). Bake for 40 minutes until the edges are crisp and set and the insides are still gooey.
5. Take out to cool for 20 minutes on the trays, then transfer carefully to wire racks or boards to cool fully (see Make Ahead).
6. For the PX sherry chocolate cream, put the chocolate, sherry and brown sugar in a large, heatproof bowl set over (but not touching) a pan of barely simmering water. Melt, stirring very occasionally, until smooth, then remove from the heat, stir in 150ml of the cream and leave to cool to just above room temperature. Whip the rest of the cream to soft peaks, then gently fold through the chocolate mixture with a balloon whisk, being careful not to overmix it or it will become grainy.
7. Spoon the chocolate cream into a piping bag and snip off the end (see tips). Put one meringue on a serving platter and pipe a third of the cream on top. Repeat with the next layers, finishing with the thicker meringue.
8. To decorate, melt the 50g chocolate and butter together (a microwave on low is fine), then cool a little. Drizzle all over the top, then scatter over the nuts. The cake is best filled as soon as you make the chocolate cream, to get a good shine (see make ahead).