For the brownie layer:

Preheat the oven to 180°C (fan 160°C)/350°F/gas mark 4. Grease or spray a 22cm (8 to 8½inch) diameter springform cake tin and line with baking paper, making sure it is at least 5 centimeters (2 inches) above the rim of the tin. Spray the paper,

To make the brownie, melt the butter and chocolate together in a heatproof bowl set over a saucepan of barely simmering water, making sure the surface of the water does not touch the bowl or using a large microwave proof bowl, melt in the microwave on defrost setting for two 2 minute intervals stirring between and after. Add the sugar, stirring until it has completely dissolved. Stir in the egg yolks.

In a clean, dry bowl, whip egg whites to soft peaks. Fold a few tablespoons of the egg whites into the chocolate mixture to lighten, then fold in the remaining whites using a rubber spatula. Spoon the mixture into the prepared tin and bake in the oven for 40 minutes. Set aside beaters and bowl.

For the meringue layer:

At about 30 minutes of time (10 minutes before the 40 is up), make the meringue topping. Whip egg whites to stiff peaks, adding the sugar a little at a time when the whites reach soft peaks, then add the vanilla extract. Sift the cornflour and cocoa powder together, then fold into the meringue by hand until the mixture is even and glossy.

Remove the chocolate brownie from the oven and very gently top with the meringue in small dollops. Smooth, making sure meringue reaches to the parchment around the edges. Return to the oven for a further 25 minutes, or until the meringue puffs up and a crust forms on the top but the centre is still quite soft. Leave to cool in the tin. The centre will collapse slightly.

Serve warm with crème fraîche or vanilla ice cream.