Sift together the flour, cream of tartar, baking soda, cornstarch, cinnamon, and salt together. Set aside.
Combine sugars and melted butter. Beat at medium speed until light and fluffy — will take a few minutes.
Add room-temp egg and vanilla extract. Beat at low to medium speed until combined.
Add dry ingredients. Mix until combined. The dough will be very thick and heavy, yet slightly crumbly.
Cover the dough tightly with plastic wrap and chill for 45 minutes
Preheat oven to 350°F. Line two large cookie sheets with parchment paper or silicone baking mats. Set aside.
Remove the cookie dough from the refrigerator and roll 1-1/2 tablespoons of dough into each ball. About 20-24 balls, give or take.