Split the sponge cakes in half and sandwich them together with jam. Arrange in the base of a 2-pint serving dish and sprinkle with the crushed biscuits. Sprinkle sherry, chopped cherries and cherry juice over sponge cakes.
Blend together egg yolks and sugar in a bowl. Warm the milk in a saucepan, then pour it on the egg mixture. Stir well, return the custard to the pan and cook over low heat (do not allow to simmer or it will curdle). When it is thick enough to coat the back of a spoon, remove from heat. Strain custard over sponge cakes and leave to set.
Just before serving, whip cream with egg whites until it forms soft peaks; spread over trifle. Sprinkle with almonds.