PREHEAT the oven to 375°F (190°C).
SIFT several cups of flour back and forth between 2 large bowls 3 to 4 times.
WEIGH 198 grams of sifted flour on a digital kitchen scale and place it in a bowl. Use 1½ cups + ½ tablespoon of flour if you don't have a scale. (Measure carefully. Spoon the sifted flour into the measuring cup and scrape the cup flat with the straight edge of a knife.)
WHISK the cream of tartar, baking soda, and salt into the flour.
CREAM ¾ cup (150 grams) of sugar and butter with an electric hand mixer on high for 1½ to 3 minutes in a separate bowl. The texture will progress from sandy to creamy. If you prefer, use a stand mixer with a paddle attachment.
BLEND the vanilla and egg into the creamed sugar and mix on medium speed for 30 seconds.
MIX the dry ingredients into the wet ingredients. Use an electric mixer on low until the flour mixture is incorporated. Scrape the sides of the mixing bowl with a rubber spatula and blend again.
STIR the cinnamon with 2 tablespoons (30 grams) sugar in a small, shallow bowl until well blended.
SCOOP the cookie dough with a 2-teaspoon cookie scoop.
ROLL the cookie dough ball in your palms until smooth. Then roll the ball in the cinnamon-sugar mixture until completely coated.
PLACE the cookie dough ball on a heavy duty aluminum cookie sheet lined with parchment paper (or a silicone mat).
REPEAT rolling the cookie dough balls and place them all on the baking sheet about 2 inches apart.
BAKE for 6 to 7 minutes until the edges are set. The middle may look slightly soft. Use your judgment here. The cookie should not be doughy. Bake until the cookies look almost done.
REMOVE the baking sheet from the oven and turn the oven off. Cool the cookies for 1 minute.
SHAPE the cookies with a cookie ring. Circle the cookie with a cookie ring larger than the cookie. Using a circular motion, swirl the cookie ring around the cookie. This will pull in the snickerdoodle sides, creating a round, uniform shape. Repeat with the remaining cookies.
PLACE the cookie sheet on the cooling rack for 5 minutes.
TRANSFER the cookies from the baking sheet to the cooling rack and allow them to cool completely (about 30 minutes).
REST the cookies. Place the cooled cookies in an airtight container for a minimum of 1 hour, but 2 to 3 hours is better.
SERVE with hot chocolate or a glass of cold milk.