Beat 4 egg whites until they hold strong peaks. Add cream of tartar and 1 cup granulated sugar, one tablespoon at a time, and beating all until very stiff. Spread in a well-buttered 9-inch pie or cake pan. (Be sure it is packed without air space.) Bake 1 hour at 275°. Beat the 4 egg yolks until very thick. Then, gradually beat in 1/2 cup granulated sugar. Add lemon juice and lemon rind. Cook over boiling water until thick. Whip the cream. When filling cools, fold in half of the whipped cream. Spread remaining on top, covering edges. Let stand 24 hours in refrigerator.