Preheat your oven to 350º
In a large bowl, mix together flour, baking soda, salt, and cream of tartar. Set aside.
In your mixer, cream together the butter, sugar, and vanilla extract.
Beat in egg, and sourdough discard until well combined.
Slowly add in bowl of dry ingredients until a dough forms.
In a shallow bowl, mix together cinnamon and sugar for coating.
Using a cookie scoop, scoop out dough balls and form with your hands. Gently roll each cookie dough ball in the shallow bowl of cinnamon sugar to coat well.
Place on a parchment lined cookie sheet at least 2 inches apart.
Bake cookies at 350º for 9 minutes. The cookies may look undercooked when you remove them from the oven, but they will continue to cook as they cool to make perfect soft, chewy cookies.
Store cookies in an airtight container at room temperature for up to three days or in the refrigerator for a week.
