Combine the flour with the baking soda, cream of tartar, and salt until well mixed.
Beat the softened butter with the white sugar and brown sugar until creamy with a hand mixer. Add the vanilla and egg then mix until well combined. Slowly add the flour mixture to the butter mixture until mixed thoroughly. Place into the refrigerator for 20-30 minutes to harden.
Preheat the oven to 350 degrees and line a baking tray with a silpat mat.
Combine the 1/4 cup of sugar with the cinnamon and mix well. Roll the dough in a small ball then toss in the cinnamon/sugar mixture. Place on the silpat mat lined baking sheet then lightly press the dough with your hand to slightly flatten. Place dough 2 inches apart on the baking sheet.
Place the baking tray into the oven and bake for 8-9 minutes. Side Note: If you like crispier cookies, cook for 9-10 minutes. Remove from the oven and let cool on the baking tray for a few minutes before transferring them to a cooling rack. Serve with ice-cold milk. Enjoy!