Cracked Sugar Cookies

found on HTEAC (adapted from AllRecipes.com)
Makes 16 3 1/2-inch cookies

10 tablespoons unsalted butter, softened
3/4 cup sugar
2 egg yolks
3/4 teaspoon vanilla extract
1 2/3 cups all-purpose flour
3/4 teaspoon baking soda
1/4 teaspoon cream of tartar
1/4 teaspoon salt

Preheat oven to 350 F (180 C). Line 2 large cookie sheets with parchment paper.
Sift together flour, baking soda, cream of tartar, and salt.
Cream butter and sugar on medium speed until fluffy, about 2 minutes. Scrape down the bowl.
Add egg yolks and vanilla, and beat for 2 more minutes.
With mixer on low speed, add the flour mixture a little at a time.
Roll 2 tablespoons of dough into a ball and roll it in some sugar. Place the dough balls 2 inches apart. Bake for 10 to 11 minutes, until tops are cracked and the edges are just brown (the centers will still be very soft). Cool on wire racks.