Margherita Sponge

100 g / 3 1/2 oz (7 tablespoons) unsalted butter, melted and cooled, plus extra for greasing

6 eggs, separated

200 g / 7 oz (1 cup) caster/superfine sugar

zest of 1 lemon, grated

800 g / 3 oz (3/4 cup) plain/all purpose flour

50 g / 2 oz  (1/2 cup) potato flour

salt

Grease a 25-cm/10-inch springform cake tin with butter and line the base with baking parchment.

Whisk the egg yolks, all but 1 tablespoon sugar and lemon rind until light then fold in the butter.

Sift the plain and potato flours and a pinch of salt on to greaseproof paper.

Whisk the whites in a grease-free bowl until just stiff. Whisk in the remaining sugar. Fold the flour and whisked whites alternately into the egg/sugar mixture.

Spread into the tin.

Bake for 30 minutes or until a cocktail stick inserted in the centre comes out clean.

Preparation time:
20 min

Cooking time:
30 min

Serves 8–10