Preheat oven to 180°C. Grease and flour a deep 23cm (9in) ring tin. Sift together flour and cornflour. Whisk egg whites and cream of tartar until soft peaks form. Gradually whisk in sugar. Fold in flour mixture and vanilla with a metal spoon.

Pour mixture into tin. Stand tin on a baking sheet. Bake for 35-40 minutes, or until the centre springs back when pressed. Invert tin onto wire rack. Allow cake to cool in tin.

For the filling, break up chocolate and melt in a heatproof bowl over a pan of simmering water. Remove from heat. Stir in soured cream and orange juice. Cool for 10 minutes.

Turn out cake. Cut into 3 layers. Sandwich together layers with filling. Put on a serving plate. For the icing, whip together cream and yoghurt until soft peaks form. Spread over the cake. Chill for 1 hour. Decorate with chocolate curls and raspberries