Cream the Butter and Sugars: Use a hand or stand mixer to beat 113 g (½ cup) softened unsalted butter, 150 g (¾ cup) granulated sugar, and 50 g (¼ cup) brown sugar together for 2–3 minutes, until light and fluffy.Add 60 g (¼ cup) thick sourdough discard, 1 large egg (room temp), and 1 tsp vanilla extract. Mix until smooth and creamy
Mix the Dough: In a separate bowl, whisk together 220 g (1 ¾ cups) all-purpose flour, ½ tsp baking soda, 2 tsp cream of tartar, ½ tsp salt, and 1 tsp ground cinnamon.Add the dry ingredients to the wet mixture and stir just until a soft, scoopable dough forms. Avoid overmixing — you want a smooth, scoopable thick dough that holds its shape.If your discard is thin, add 1–2 tablespoons of extra flour until the dough feels thick and holds together well.
Roll in Cinnamon Sugar: In a small bowl, combine 3 Tbsp granulated sugar and 1 ½ tsp ground cinnamon for the coating.Scoop 40 g (2 Tbsp) portions of dough, roll into balls, and coat well in the cinnamon-sugar mixture. You’ll get about 16 cookies at this size.
Bake: Place dough balls 2 inches apart on a parchment-lined baking sheet.Bake at 350°F (175°C) for 11–13 minutes, until the edges are set but the centers still look slightly soft.
Let cool on the pan for 5 minutes before transferring to a wire rack to finish cooling.
Notes
I always recommend using a kitchen scale for accuracy when measuring ingredients. The cup measurements are approximate and may yield inconsistent results.