Preheat oven to 350F. In mixing bowl, combine sugar, flour and salt. Stir in lemon juice rind, beaten eggs yolks, butter and milk. Beat egg whites till stiff but not dry; fold into lemon mixture. Pour into buttered 6 cup casserole. Place in larger pan, pour in hot water to about 1" depth. Bake in 350F oven for 40 minutes or till topping is golden brown. Serve warm.
