Cut a thick loaf of sponge cake, bought at the confectioner's, horizontally into four parts. Put between alternate layers liberal instalments of tart and sweet fruit jelly, such as currant or grape and crab-apple. Fit the slices smoothly into place and cover the whole cake with an icing made by whipping stiff the whites of four eggs with enough powdered sugar to make a consistent frosting. Set in the oven for five minutes to harden, but not to color, then in a sunny window. You can make this in one-tenth of the time required for a regular jelly cake. Angel cake, or any good plain loaf, is suitable for this purpose.