In a large bowl, cream butter and sugar until light and fluffy. Beat in the egg, concentrate and orange zest. Combine dry ingredients; gradually add to creamed mixture and mix well. Cover and refrigerate for 2 hours.
Divide dough in half. On a lightly floured surface, roll out each portion to 1/8-in. thickness. Cut with a floured 2-in. round cookie cutter.
Place 2 in. apart on greased baking sheets. Bake at 350° for 6-7 minutes or until edges begin to brown. Remove to wire racks to cool.
Combine all the frosting ingredients until smooth. Place in a heavy-duty resealable plastic bag; cut a small hole in corner of bag. Pipe polka dots on cookies.