Preheat oven to 350 degrees F. Cream together butter and sugar until it is nice and creamy. Mix in 1 egg yolk at a time and vanilla extract. Add flour, baking soda, cream of tarter, and salt until cookie dough is completely mixed. Be sure to scrape down the bowl to be sure everything is mixed. Using a medium scoop, form dough balls and roll them in sugar crystals. Place cookie balls on a cookie sheet lined with parchment paper 2 inches apart from one another. Be sure not to flatten the dough. Bake for 12-14 minutes until the surface of each cookies have a cracked like texture. Remove from oven and allow cookies to remain on the cookie sheet for 5 minutes before transferring to a cooling rack.