Step 1: Mix Ingredients
Preheat oven to 300ºF. In a large mixing bowl, beat ½ cup softened butter and ½ cup shortening with an electric mixer on medium to high speed for 30 seconds. Add 2 cups sugar, 1 tsp baking soda, 1 tsp cream of tartar, and a pinch of salt. Beat mixture until combined, scraping sides of bowl occasionally. Beat in 3 egg yolks and ½ tsp vanilla. Beat in as much of the 1¾ cups flour as you can with the mixer. Stir in any remaining flour.
Step 2: Shape & Bake
Shape dough into 1-inch balls. Place balls 2 inches apart on ungreased cookie sheets. Bake for 12 to 14 minutes or until edges are set; do not let edges brown. Cool cookies for 2 minutes on cookie sheet. Transfer cookies to wire racks and let cool.
Test Kitchen Tip
Tender and sweet sugar cookies offer welcome canvases for flavor artistry. Add dashes of new flavors -- spices, shredded citrus peel, or extracts -- to make your cookies distinct.
How to Store Sugar Cookies
Layer cookies between waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months.