Preheat the oven to 375 degrees Fahrenheit, and line a cookie sheet with parchment paper.
Cream together the granulated sugar, powdered sugar, butter, shortening, eggs, and vanilla using a stand mixer until pale and fluffy. Set aside.
In a large mixing bowl, sift together the dry ingredients... flour, salt, baking soda, and cream of tartar.
Slowly add the dry ingredients to the creamed sugars, until a dough forms. As it thickens, you may want to knead it with your hands rather than using the mixer.
Chill the dough in the refrigerator for at least 30 minutes, or overnight in an air-tight container.
Once the dough has chilled, roll it into consistent one inch balls. Before transferring the dough to your prepared cookie sheet, roll each ball in granulated sugar.
Using a flat bottomed or patterned glass, press the cookies until they are about 1/4″ – 1/2″ thick.
Sprinkle them with additional granulated sugar before transferring them to a hot pre-heated oven.
Bake the cookies at 375 degrees for 8 to 12 minutes- or until the bottoms are golden brown. You don’t want the tops to turn too brown or they’ll end up too crunchy. Keep a close eye on your first batch to dial in your exact baking time!
Pull the baked cookies from the oven and transfer to a cooling rack.
Store in an airtight container for up to 5 days. Enjoy!