1. Preheat oven to moderate (325° F.).
2. Roll the zwieback into fine crumbs. Grease a nine-inch spring-form pan and dust the sides with zwieback crumbs. Mix the remaining crumbs with one-quarter cup of the sugar and the butter and press onto the bottom of the pan. Bake five minutes. Cool.
3. Press the cottage cheese through a fine sieve. Add half the remaining sugar, the flour, salt, egg yolks, sour cream, lemon rind and juice. Whip until thoroughly blended.
4. Beat the egg whites until stiff, adding the remaining sugar gradually. Fold into the cheese mixture.
5. Turn the mixture into the prepared pan and bake at 325° F. about one and one-half hours. Cool in the pan and glaze as directed.