Roughly chop the tangerines. In a bowl, toss the tangerines with the madeira until thoroughly coated, then set aside to macerate.

Heat othe oven to 110C/90C fan/gas ¼. Line two baking sheets with baking parchment. Whisk the egg whites in a clean bowl or stand mixer until soft peaks form. Without stopping whisking, gradually add the sugar and whisk until thick and glossy, then whisk in the vinegar too. Toss the walnuts in the melted chocolate, then fold into the egg so the meringue is marbled with chocolate.

Spread a circle of the chocolate and walnut meringue about 20-25cm in diameter on each baking sheet. Bake for 2 hrs until crisp but slightly soft in the middle – don’t worry if it cracks; it will still taste delicious. Remove from the oven and carefully lift the meringues and parchment onto wire racks to cool. Peel the parchment from the meringues, then use a wide palette knife to lift one meringue onto a serving platter or cake stand.

Whip the cream to soft peaks, being careful not to over whip. Fold in half the tangerines and the madeira used to soak them. Spread just over half the cream mixture onto the meringue, then top with the other layer of meringue, the remaining cream and the rest of the tangerines. Sprinkle over the grated dark chocolate and serve. Can be made a day ahead and chilled in the fridge.