Preheat the oven to 350 degrees. In a bowl beat butter with sugar until fluffy. Add the salt, the vanilla, and the egg yolk, and beat the mixture until it is smooth. Add flour and beat until just combined.
Pack the dough into a cookie press fitted with various designs and press cookies 1 inch apart onto ungreased baking sheets. Sprinkle with decorating sugars and bake for 12 to 15 minutes or until golden. Cool cookies on a rack.