Line a 12-section bun tray with paper cake cases. Put all the cake ingredients in a bowl and beat with a hand-held electric whisk for about a minute until light and creamy. Divide the cake mixture between the paper cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes or until risen and just firm to the touch.
Meanwhile, beat the egg whites in a thoroughly clean bowl until peaking. Gradually beat in the sugar, a tablespoonful at a time, to make a firm, glossy meringue.
Remove the cakes from the oven and raise the temperature to 230°C (450°F), Gas Mark 8.
Scoop out about 1 teaspoon of sponge from the top of each cake and fill with the lemon curd. Pile up the meringue on top, swirling it with a palette knife. Return to the oven for a further 1–2 minutes, watching closely, until the meringue is beginning to brown. Serve warm.