These are the BEST Snickerdoodles! They're soft and chewy, perfectly sweet and they have just the right amount of cinnamon. Chances are they'll become a new favorite cookie, everyone always loves these!
In a mixing bowl whisk together flour, baking soda, cream of tartar and salt for 20 seconds, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment cream together butter, 1 cup granulated sugar and brown sugar until combined.
Mix in egg then blend in egg yolk and vanilla. Add in flour mixture and mix just until combined.
In a small bowl whisk together 2 1/2 Tbsp granulated sugar with the cinnamon.
Scoop dough out 2 Tbsp at a time and shape into balls. Roll each cookie dough ball in the cinnamon sugar mixture to thoroughly coat.
Transfer to plates, cover and chill 30 minutes to 1 hour (so cookies spread less). Preheat oven to 350 degrees during last 15 minutes of cookies chilling.
Transfer 12 dough balls to a 18 by 13-inch baking sheet lined with parchment paper or a silicone liner, spacing them 2-inches apart (keep remaining chilled).
Bake cookies in preheated oven 9 - 10 minutes, or until nearly set but centers are soft (they should appear slightly under-baked).
Remove from oven and cool on baking sheet several minutes then transfer to a wire rack to cool. Repeat with remaining dough balls. Store cookies in an airtight container.
Notes
*If you are closer to sea level or if you're cookies aren't normally prone to spreading reduce flour to 2 1/2 cups.