Pre-heat oven to 350℉
Prepare to baking sheets with parchment paper
Brown the butter over medium heat, stirring often. Keep a close eye so it doesn’t burn—it's ready when it turns golden and smells rich and nutty.
Pour the browned butter into a glass measuring cup and let it cool slightly before refrigerating. Chill for about 45 minutes, stirring every 10 minutes or so, until the butter reaches 75°F. It should still be liquid at this stage.
Spread the pumpkin purée onto a plate and blot with paper towels to absorb the excess liquid. Continue blotting until the pumpkin has a playdough-like consistency and measures about ⅓ cup.
When the butter has cooled, whisk in the sugar for about 1 minute, until well combined and slightly thickened.
Whisk in the egg yolk, vanilla, and prepared pumpkin purée until fully blended.
Stir in the dry ingredients, just until blended.
Place in the refrigerator for 5-10 minutes.
In a small bowl, combine the cinnamon and sugar for rolling.
Scoop the dough into golf ball–sized portions, then roll each one in the cinnamon-sugar mixture to coat.
Place the dough balls on the prepared baking sheet and gently flatten them. Sprinkle with a little extra cinnamon sugar, then bake for 10–12 minutes, until the edges are crisp and the centers are puffy.
Cool and enjoy!