Cream butter, gradually add sugar and beat until light and fluffy. Beat in egg, milk and vanilla. Combine flour, baking powder and salt. Gradually add to creamed mixture. Chill before handling. Roll out dough to 1/8" thickness on lightly floured surface. Cut with cookie cutters, dipped in flour. Bake on an ungreased cookie sheet at 350 degrees for 8-10 minutes or until lightly browned. Cool slightly and then remove to wire racks to cool. Makes 4 dozen.