Preheat oven to 350 degrees.
In a mixer, cream butter, cream cheese and white and brown sugars.
Beat in egg yolks and vanilla.
Remove from mixer and stir in flour, baking soda and cream of tartar.
Using a tablespoon, scoop the cookie dough and drop onto a non greased cookie sheet about 2 inches apart.
Bake for 15 minutes at 350 degrees.
Calories: 103kcal | Carbohydrates: 13g | Protein: 1g | Fat: 4g | Saturated Fat: 2g | Cholesterol: 28mg | Sodium: 70mg | Potassium: 23mg | Sugar: 7g | Vitamin A: 160IU | Calcium: 7mg | Iron: 0.5mg