Beat butter at medium speed with an electric mixer until creamy. Gradually add brown sugar, beating well. Add egg and vanilla and continue beating.
Combine flour, baking soda, and salt. Add to the butter mixture a little at a time and beat until well blended.
Preheat oven to 350F.
Roll dough to ¼ inch thickened between 2 sheets of wax or parchment paper. Cut into favorite shape, stars for me. Place 1 inch apart on ungreased baking sheets. Sprinkle cookies with decorator crystals.
Bake for 10 to 12 minutes or until golden. Let cookies cool on baking sheet for a minute. Transfer carefully to a wire rack to cool completely.