Stir sugar into milk until dissolved. Add grated lemon rind and juice. Blend well. Freeze for one hour in two freezer trays (or use loaf pans or a Pyrex bowl), or until ice crystals form around edge. Beat egg whites until stiff. Whip cream. Combine cream with egg whites; then add to frozen mixture in large bowl of electric mixer. Add salt. Beat just until the mixture is well blended. Return to freezer. Freeze for 3 hours, or until firm.