For the currant cake, cream margarine with yolks and half the amount of sugar. Beat the egg whites with the remaining sugar until stiff, stir together with flour, vanilla and lemon zest.
Spread the dough on a greased and dusted baking sheet and sprinkle densely with currants. Bake the currant cake for 30 minutes.
Beat the 3 egg whites and sugar until very stiff. Spread the mousse over the cake and briefly bake the currant cake again.