Slightly crispy on the outside, with an incredible chewy texture on the inside, these cookies are a classic in large part thanks to their fantastic texture. Warm from the oven and gently spiced with cinnamon and sugar, a well-made Snickerdoodle is one of the best cookies around.
For the dough: In a large bowl, add the flour, cream of tartar, baking soda, Kosher and sea salts. Mix until combined and set aside. In the bowl of a stand mixer fitted with the paddle attachment, mix the butter on medium speed for 5 to 10 seconds. Add the sugars and beat until the butter mixture is aerated and pale in color, approximately 4 minutes. Scrape the sides and bottom of the bowl with a rubber spatula to bring the batter together. Crack eggs into a small cup or bowl and add the vanilla. With the mixer at medium speed, add eggs and vanilla to the butter mixture, one egg at a time, mixing the first briefly before adding the second, until the batter resembles cottage cheese, approximately 5 seconds for each egg. Scrape the sides and bottom of the bowl with a rubber spatula to bring the batter together. Mix on medium speed for 20 to 30 seconds, until just combined. Add dry ingredients all at once and mix on low speed until dough comes together but still looks shaggy, approximately 30 seconds. Do not overmix. Remove the bowl from the stand mixer. With a plastic bench scraper, bring the dough completely together by hand.
Assemble the cookies: Preheat the oven to 350 degrees F. Line sheet pans with parchment paper. Make the coating by mixing the sugar and cinnamon in a bowl, ensuring there is plenty of room in bowl to roll dough in sugar. Using an ice cream scoop, portion dough into 24 mounds and roll into balls. Coat each ball completely in cinnamon sugar. Evenly space balls on the lined sheet pans.
Bake cookies 10–12 minutes. After 8 minutes, rotate the pan and bake until the tops are barely set and the edges are lightly golden, another 2–4 minutes. When the cookies are done, slap the pan against a hard surface to “settle” them and cool in the pan. Using a metal spatula, transfer the cookies to a wire rack to further cool completely. Repeat with the remaining dough.