In a large bowl, cream shortening and sugar until light and fluffy. Beat in the egg, milk, orange zest and vanilla. Combine the flour, baking powder and salt; gradually add to the creamed mixture and mix well.
On a lightly floured surface, roll out to 1/4-in. thickness. Cut with 2-1/2-in. cookie cutters dipped in flour. Place 1 in. apart on greased baking sheets. Bake at 375° for 6-8 minutes or until lightly browned. Remove to wire racks to cool.
In a large bowl, beat the butter, confectioners' sugar, vanilla, orange zest and enough orange juice to achieve spreading consistency. Add food coloring if desired. Frost cooled cookies.
Editor's Note: Instead of rolling and cutting out these cookies, the dough may be dropped by tablespoonfuls onto greased baking sheets. Bake and frost as directed.