Set racks in the upper and lower thirds of the over and preheat to 375 degrees.
In the bowl of a standing electric mixer fitted with the paddle attachment, beat together on medium speed the butter, sugar, salt, and vanilla until very light and fluffy, about 5 minutes. Beat in the egg yolks, 1 at a time, beating smooth after each addition. Scrape down the side of the bowl and beater. On low speed, add the flour and mix only until it is completely absorbed. Remove the bowls from the mixer and finish mixing the dough with a large rubber spatula.
Insert a die into the cookie press, then fill it with about a quarter of the dough. Press the cookies out onto the prepared pans, leaving 1-inch around all cookies. Bake the cookies for 10 to 12 minutes, or just until they are a very pale golden color. Slide the paper from the pans onto the racks. If desired, decorate with bits of candied fruit, raisins or nuts; make into sandiwches with ganache or melted milk chocolate; or dip partially into chocolate that may further be dipped into chopped nuts or shaved chocolate. Store the cooled cookies between sheets of parchment or waxed paper in a tin or plastic container with a tight-fitting cover.
Recipe courtesy of Nick Malgieri, Cookies Unlimited