1. In a medium bowl, place egg whites, let stand at room temperature for 30 minutes.

2. Beat with an electric mixer on high speed until soft peaks form (tips curl).

3. Set beaten egg whites aside.

4. In a large mixing bowl, combine egg yolks, lemon peel, lemon juice, and melted margarine.

5. Beat with an electric mixer on high speed till well mixed.

6. In another mixing bowl, combine sugar, flour, and salt.

7. Using electric mixer on low speed, add sugar mixture to egg yolk mixture alternately with skim milk , beating just till combined after each addition.

8. Fold about one-third of the flour mixture into the egg whites.

9. Then fold egg white mixture into the remaining flour mixture.

10. Pour into a 2-quart square baking dish.

11. Place baking dish in a large baking pan; pour hot water into baking pan around baking dish to a depth of 1 inch.

12. Bake in a 350* oven about 40 minutes or till top is golden brown.

13. Remove large pan from oven.

14. Carefully lift the baking dish from the water; transfer to a wire rack.

15. Serve warm.

16. Top with frozen yogurt or ice milk, if desired.