Chocolate-hazelnut meringue cake

1.Preheat oven to 160°C. Butter a 21cm-diameter springform cake tin and line base and sides with baking paper. Melt chocolate and butter in a bowl over a saucepan of simmering water, stirring occasionally until smooth (2-3 minutes), then remove from heat.

2.Whisk egg yolks, sugar and vanilla in an electric mixer until pale and fluffy (4-5 minutes). Fold in chocolate mixture, then sift in flour, cocoa and baking powder, add hazelnut meal and fold to combine. Pour into prepared tin and smooth top.

3.For choc-hazelnut meringue, whisk eggwhites and a pinch of salt in an electric mixer to soft peaks (4-5 minutes). Gradually add sugars, whisking until mixture is glossy, then sift in cocoa and cornflour, add hazelnut meal and fold to combine. Spoon onto chocolate mixture, forming peaks and swirls, then bake until meringue is crisp (1 hour 15 minutes to 1 hour 20 minutes). Cool to room temperature, then carefully remove the sides of the tin. Dust with extra cocoa, scatter with hazelnuts and chocolate curls and serve with crème fraîche.