In a medium bowl combine the flour and salt with a wire whisk. In a large mixing bowl cream the butter and sugar with an electric mixer on medium speed. Add the egg and vanilla, and beat until well blended. Scrape down sides of bowl, then add the flour mixture. Blend on low speed just until combined. Do not overmix.
Gather dough into a ball. Flatten the ball into a disk and wrap tightly in plastic wrap or a plastic bag. Refrigerate one hour until firm.
On a floured surface, roll out dough to a 1/4 inch thickness. With cookie cutters, cut dough into desired shapes and place on ungreased cookie sheets. Decorate with colored sugars or sprinkles. Bake for 13-15 minutes, being careful not to brown. Immediately transfer cookies with a spatula to a cool, flat surface.