In mixing bowl, cream butter, cream cheese, and sugar. Beat in egg and vanilla. Combine flour and salt in a seperate bowl. Gradually beat flour mixture into creamed mixture. Cover and refridgerate for 2 hours.
On a lightly floured surface, roll out the dough to 1/4 inch thickness. Cut with cookie cutter. Place 2 inches apart on an ungreased cookie sheet. Sprinkle with colored sugar. Bake at 375 for 8-10 min. Remove and cool on wire racks.