Lime Sandwich Sugar Cookies

In a large bowl, cream together the butter and sugar until smooth. Beat in the eggs one at a time, then stir in the vanilla. Combine the flour, baking powder and salt; stir into the creamed mixture until well blended. Cover or wrap dough, and refrigerate for at least 2 hours. If you are in a big hurry, freeze for a half hour. Preheat oven to 350 degrees F (175 degrees C). On a lightly floured surface, roll the dough out to 1/4 inch in thickness. Cut into desired shapes with cookie cutters. Place cookies 1 1/2 inches apart onto ungreased cookie sheets. Bake for 7 to 8 minutes in the preheated oven. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely. For the frosting: In a medium bowl, beat the lime juice, milk, confectioners' sugar and green food color until smooth and creamy. Add more milk or sugar if necessary to achieve a good spreading consistency. When cookies are completely cool, spread icing between cookies to make sandwiches.