1Heat oven to 350°F. Lightly grease bottom only of 15x10x1-inch pan with shortening. In large bowl, beat butter, 2/3 cup powdered sugar, 2 tablespoons lemon peel, 1 tablespoon lemon juice and 2 drops food color with electric mixer on medium speed until creamy, or mix with spoon. Stir in flour until well blended. Press in pan, using floured fingers (flour fingers several times to prevent sticking).
2Bake 20 to 25 minutes or until light golden brown.
3In medium bowl, mix all glaze ingredients until smooth and spreadable. Pour glaze over warm bars; spread evenly (glaze will be very thin). Cool completely, about 1 hour. Bars are very tender; remove from pan using very flat-edged metal pancake turner. For bars, cut into 8 rows by 8 rows.