Preheat the oven to 170°C/150°C fan oven/Gas Mark 3. Grease and baseline an 18 cm (7 in) square cake tin with non-stick baking parchment. Sift the flour, cornflour and 50 g (2 oz) of caster sugar into a bowl. Set aside.

Whisk the egg whites with the salt, cream of tartar, vanilla extract, rosewater and 1 tablespoon of cold water until stiff. Gradually whisk in the remaining sugar and continue to whisk until stiff and glossy. Sift the flour mixture over the egg whites and carefully fold in with the crushed cardamom seeds and grated lemon rind. Spoon into the prepared tin and level the surface.

Bake for 35 minutes or until firm to the touch and the cake has shrunk from the sides of the tin. Loosen round the sides with a palette knife and flip the tin upside down on to a cooling rack, leaving the cake in the tin to cool. Lift off the tin and cut the cake into nine squares, then halve each one to make 18 triangles. Serve plain or with fromage frais, berries and pineapple, and dusted with icing sugar.