To make the sponge whisk the egg whites in a large, clean bowl, until they stand in firm, snowy peaks.

Gradually sift and beat in the sugar until the mixture is satiny and smooth; mix in the zest. Lightly whisk the egg yolks separately, then beat them into the meringue a spoonful at a time and continue to blend them in well.

Sift over one-third of the flour and gently fold it in using a large metal spoon; fold in the rest of the flour in two stages.

Pour the mixture into a greased and floured 22 cm ( 8 1/2 in spring-form tin and bake at  (350°F) Gas 4 for 40 minutes until well risen and golden. Cool on a wire rack.

Meanwhile make the filling. Steep the candied peels, sultanas and candied fruits in a bowl with the rum for 1 hour, mixing it every now and then. Bring the milk to the boil with a split piece of vanilla pod, draw off the heat and leave to infuse and cool. Remove the pod.

Whisk together the caster sugar and the egg yolks in a heat-proof bowl, sprinkle over the gelatine powder and gradually pour on the cooled milk, whisking all the time. Place the bowl over a pan, a quarter filled with simmering water, and stir gently while the custard cooks and thickens. Set aside to cool.

Whip the cream until softly peaked. Beat the vanilla custard until smooth and creamy, then fold it into the whipped cream together with the soaked fruits and rum. Leave to chill for 1 hour.

Cut the sponge into three layers. Reserve about one-third of the cream for the top and the sides of the cake and use the rest to fill the two layers. Cover the top and sides of cake with the rest of the cream, then decorate with pieces of fruit. Chill for 3 - 4 hours before serving.