Snickerdoodle Cookies that are thick, soft, and coated in cinnamon sugar. Slightly crisp at the edges with chewy centers and a classic buttery flavor that makes every bite perfectly nostalgic.
In a large mixing bowl, cream the butter, dark brown sugar, and granulated sugar together until light and fluffy.
Add the egg and mix until incorporated, then add the yolk and mix until incorporated.
Add the vanilla and mix again until smooth.
In a separate bowl, whisk together the flour, cinnamon, baking soda, cream of tartar, cornstarch, and salt.
Add the dry ingredients to the wet mixture and mix until no streaks of dry flour remain. Do not overmix.
Scoop or portion the dough so each cookie is about 80 grams and shape as smooth balls.
Mix the rolling sugar and cinnamon in a small bowl. Roll each dough ball in the mixture to coat evenly. Place them on a lined tray.
Cover the tray well so the dough does not dry out and refrigerate for at least 3 hours, but I recommend 6-12 hours for best results.
Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper and arrange the cookies with at least 3 inches (8 cm) of space between each one.
Bake for 12 minutes, or until the edges are lightly golden and the centers appear just set.
Remove from the oven and, while the cookies are still hot, use a 4-inch round cookie cutter to gently swirl around each cookie, tucking in any uneven edges to form a clean, round shape. The gentle motion helps shape them into perfectly round bakery-style cookies.
Sprinkle a little of the cinnamon sugar mix on top.
Allow cookies to cool on the baking sheet for 10 minutes before transferring to a wire rack to finish setting.