1. Set the refrigerator control for fast freezing.
2. Beat the egg whites until stiff but not dry. Gradually beat in the sugar.
Add, while beating, the corn syrup, milk, lemon rind and juice. Pour into freezer tray and freeze until almost firm.
3. Turn into a cold bowl, break up the lumps and beat with a rotary hand or electric beater until smooth. The mixture should be mushy but not melted. Turn again into the tray and freeze until firm.