Beat the egg yolks, lemon juice, lemon rind, and butter or margarine together until the color is thick and lemon. Combine sugar, flour, and salt; add milk to the yolk mixture in turn and beat well after each addition.
Beat egg whites till they are stiff. Mix egg whites into the batter with an electric mixer at low speed. Pour into a baking dish of 8 inches in line.
Add a pan of hot water in the oven, and put the baking platter in the pan. Bake for 45 minutes, at 350 degrees.
