In large bowl, cream butter, sugar and salt with electric mixer until light and fluffy. Add egg yolks one at a time, mixing well after each addition. Add vanilla. Add flour: mix just until combined. (Note: Dough can be tinted with Wilton Icing Color. Add small amounts until desired color is reached.) Divide dough in half. Press dough to flatten; wrap with plastic wrap. Refrigerate at least 2 hours or overnight.