Preheat your oven to 350°F.

In a medium-sized mixing bowl, whisk together the flour, baking soda, salt, and cream of tartar, until evenly mixed. Then, set the bowl aside.

With an electric mixer or stand mixer, cream together the sugar and room temperature butter in a large mixing bowl until they are fully light and fluffy, scraping down the sides as needed, about 5 minutes.

Add the egg, egg yolk, and sourdough discard to the bowl. Beat the mixture until until it is creamy and well combined, about one minute.

Add the dry ingredients to the wet mixture, and stir until a tacky dough forms.

In a small bowl prepare the cinnamon-sugar coating by whisking together the cane sugar and ground cinnamon.

Scoop and roll the cookie dough into 2-inch balls. For uniform cookies, you can weigh each portion of cookie dough out to 55g. The dough will be quite soft, flouring your hands and working quickly will help to prevent sticking.

Generously coat each cookie dough ball by rolling it in the cinnamon-sugar mixture, and space them 3 inches apart on a parchment-lined baking sheet.

Bake the cookies in batches on the center rack of your oven for 9-11 minutes. It’s important to note that the cookies may appear underdone when you take them out of the oven. Resist the temptation to cook them longer.

Once you remove the cookies from the oven, let them cool for at least 10 minutes before transferring them to a cooling rack to finish cooling. Allowing them to fully cool will help them set and achieve a perfectly soft and chewy texture.