Chill can milk in ice tray until almost frozen around edges. In large bowl mix egg yolk, 3 tablespoons sugar, lemon rind and 1 tablespoon lemon juice. Beat until stiff, egg white and gradually beat in 2 tablespoons sugar. Fold egg white mixture into egg yolk mixture. Whip milk in cold bowl until fluffy. To this add 1 1/2 tablespoons lemon juice and whip stiff. Fold into egg mixture. Put into ice tray and sprinkle graham cracker crumbs over top. Freeze in ice tray. Do not stir. Serves 4.