In a medium mixing bowl combine sugar, flour and salt.
Stir in lemon juice and rind, butter and milk.
Beat
egg yolks until thick and pale, and add to the lemon
mixture.
Beat
egg whites until stiff but not dry, and fold into the
lemon mixture.
Pour
into a buttered 6 cup casserole. Place in a larger pan.
Pour hot water to about 1 inch deep in the larger pan.
Bake
at 350 degrees F. for about 40 minutes, until the topping
is set and golden. Serve warm.