Beat butter and shortening at medium speed with an electric mixer until creamy. Gradually add sugar, beating well. Add eggs and milk, beating until blended.
Combine flour and next 3 ingredients. Add to butter mixture, beating at low speed just until blended; stir in lemon rind and juice. Divide dough into 4 equal portions; wrap each in plastic wrap, and chill at least 2 hours or up to 6 hours.
Roll 1 dough portion to a 1/4-inch thickness on a lightly floured surface. Cut with a 3-inch heart-shaped cookie cutter, and place on lightly greased baking sheets. Repeat procedure with remaining dough portions.
Bake at 350° for 8 to 9 minutes or until lightly browned on bottoms. Let cool on baking sheets 2 minutes; remove to wire racks, and cool 20 minutes or until completely cool.
Remove and reserve about 1/4 cup Icing. Tint remaining Icing with green food coloring. Spread green-tinted icing on tops of cookies. Tint reserved 1/4 cup Icing with orange food coloring, and spoon into a zip-top plastic bag. Snip 1 corner to make a small hole; pipe dots on cookies.
Note: To make ahead, bake and cool cookies as directed. Do not frost. Place in airtight containers, and freeze up to 1 month. Thaw and frost as directed.
Prep: 30 min., Chill: 2 hr., Bake: 9 min. per batch, Cool: 22 min.