First, make the crémeux. Bring the milk and cream to the boil in a small saucepan, whisking occasionally. Whisk the egg yolks and sugar together in a medium heatproof bowl until smooth. Pour in the hot cream mixture in a steady stream, whisking continuously until combined. Return to the saucepan, and simmer over a low heat for 3-4 mins, stirring continously until thickened to a custard.
Put the dark chocolate into a large heatproof bowl and strain the hot custard over it through a fine mesh sieve, whisking until the chocolate has melted and the mixture is smooth. Leave to cool for 5 mins until just warm. Add the butter and blitz using a hand blender until smooth. Cover and leave at room temperature until needed.
Heat the oven to 150C/130C fan/gas 2 and line two baking sheets with baking parchment. For the meringue, beat the egg whites in a large, clean bowl using an electric whisk or in a stand mixer until soft peaks form, then gradually beat in the sugar, 1 tsp at a time, until the meringue is thick and glossy. Whisk in the vinegar and cornflour.
Spoon half the meringue mixture into the middle of one of the prepared baking sheets, and spread out into a roughly 20-25cm circle. Repeat with the the remaining meringue mixture on the second baking sheet. Drizzle the melted chocolate evenly over both circles, then gently swirl it using a cutlery knife or skewer until you have a marbled effect. Bake for 1 hr, turn off the oven and leave the meringues to cool completely inside.
Meanwhile, make the candied peanuts. Tip the peanuts, sugar and 1 tbsp water into a heavy-bottomed saucepan and cook over a medium heat for 3-4 mins, stirring until the peanuts start to crystallise and turn white. Continue to cook, stirring, for another 3-4 mins until the peanuts turn dark brown. Sprinkle with a pinch of sea salt flakes, then scrape onto a sheet of baking parchment. Spread out using a spatula, and leave to cool completely.
For the peanut butter cream, melt the white chocolate, peanut butter, butter and 25ml cream in a small saucepan over a low heat, stirring until smooth. Transfer to a bowl and leave to cool for 10 mins. Whisk the remaining cream to soft peaks, then fold in the peanut butter mixture until thick and billowy.
To assemble, put one meringue circle on a serving plate, spoon over half the crémeux followed by half the peanut butter cream, then sprinkle with half the candied peanuts. Top with the second meringue circle, then the remaining crémeux and peanut butter cream, and the rest of the candied peanuts. Scatter over some dark chocolate shavings, if you like. Will keep chilled for up to two days.