Maple Snickerdoodles

In a large bowl, beat the softened butter, 1/2 cup granulated sugar, and brown sugar with a mixer on medium speed for 3–4 minutes, until pale and fluffy. Scrape down the sides as needed.
Reduce speed to low. Add maple syrup, vanilla extract, egg, and egg yolk—one at a time—mixing just until combined and glossy.
In a separate bowl, whisk together the flour, cornstarch, baking soda, 1 1/2 teaspoons cinnamon, cream of tartar, and salt. Ensure no clumps remain.
Add the dry ingredients to the wet mixture in stages, mixing gently on low just until a soft dough forms. Do not overmix.
Cover bowl and chill dough in the refrigerator for 30–60 minutes.
While dough chills, mix together 1/4 cup granulated sugar and 2 teaspoons cinnamon in a small bowl for rolling.
Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.
Scoop chilled dough into 2-tablespoon balls. Roll each ball in cinnamon sugar until evenly coated.
Arrange dough balls on prepared baking sheets, spacing 2 inches apart. Bake for 9–12 minutes, until edges look set but centers are still soft.
Let cookies cool on the tray for 5 minutes, then transfer to a wire rack to cool completely.