Line the base and sides of a 23cm springform cake tin with baking parchment. Melt 240g dark chocolate with 180g unsalted butter
and stir until smooth, then let cool a few minutes. Beat 2 whole eggs and 4 egg yolks with 90g light brown sugar and 1 tsp vanilla extract
until pale and thick, then add the chocolate mixture, 50g sifted plain flour, 40g ground almonds and ½ tsp baking powder, folding gently to mix.
Pour into the tin and bake for 35-40 minutes in a preheated 160°C oven. Remove from the oven and let cool slightly. Then increase the
oven temperature to 180°C. Whisk the 4 remaining egg whites until soft peaks form, then add 220g caster sugar in stages, 1 Tbs at a time
and whisking each Tbs for 30 seconds before adding more. Whisk in 1 tsp white wine vinegar, then gently fold in 3 tsp of sifted cornflour
and 25g of sifted cocoa powder, until well combined. Spoon the meringue mixture onto the cake, spreading evenly, and return to the oven
to bake for another 20-25 minutes, until the meringue is crisp. Let cool in the tin for 20 minutes, then gently run a knife around the
inside edge of the tin and remove the ring. Let cool to room temperature and chill for 2 hours. Dust with extra cocoa powder before serving.