In a medium bowl, beat together butter, sugar, egg, milk and vanilla until light and fluffy. Add flour, baking powder and salt, beating until blended.
Preheat the oven to 375 deg F/190 C (350 deg F/170 C, if using a convection oven). On a lightly floured surface, roll dough 1/4 inch thick. with lightly floured cookie cutters, cut into desired shapes and decorate with sugar crystals,. Place 1 inch apart on ungreased cookie sheets.
Bake 7 - 10 minutes (6 -7 for convection oven) or until edges just start to go golden. Remove cookies from cookie sheets; cool on racks or parchment paper.
Let stand until cooled. Will keep in cookie tins for about 2 weeks (but good luck making them last!). Makes 48 cookies.