Mix wet ingredients in a large bowl. (16 tbsp unsalted butter, 1½ c granulated sugar, 2 large eggs) This will be your main dough bowl later on.
Whisk together dry ingredients in a medium bowl. (2¾ c AP flour, 2 tsp cream of tartar, 1 tsp baking soda, ¼ tsp salt)
Pour dry ingredients into wet ingredients and mix.
Mix topping ingredients (½ c granulated sugar, 2 tsp cinnamon). Preheat oven to 350 °F.
Scoop 2 tbsp of dough at a time and roll into a ball. Roll ball in cinnamon sugar and space evenly on a cookie sheet.
Bake on 350 °F for 8-10 minutes, until edges are gently set and the middles are puffy and soft. For a soft and chewy snickerdoodle cookies should look underbaked.
Allow cookies to finish baking and cool on cookie sheet. Enjoy while hot.
Notes
Cookies will become a bit more crunchy after refrigerating.