Step 1
Preheat oven to 325°F. Line 2 half sheet pans with parchment paper.
Step 2
In a large bowl of an electric mixer beat sugar, butter, and shortening at medium speed for 2 minutes. Add baking soda, cream of tartar, and salt. Beat mixture until combined. Beat in egg and vanilla. Add flour and mix until combined.
Step 3
Using a small ice-cream scoop, drop dough onto lined sheet pans. Flatten slightly with hand. Sprinkle the additional 2 tablespoons of sugar on top of the cookies. Bake for 8 minutes. Let cookies rest for 5 minutes. Remove from cooking sheets to cooling racks.