Preheat oven to 350F, sprinkle 2 baking sheets with oil or cover with parchment paper.Whisk the softened butter and sugar until creamy.
Add yolks, then vanilla beat.
Add flour, baking soda, and cream of tartar. Whisk until smooth.
Scoop up walnut-sized balls of dough and place on a baking sheet 2 inches apart.
Bake for 10-11 minutes until the top of the cookie is cracked. Remove from the oven, let the cookies cool and remove from the baking sheet.