Brown the Butter: In a large stainless steel pan, over medium heat, melt the unsalted butter while stirring occasionally until it develops a nutty aroma and golden brown bits, then remove from heat. Chill until it reaches 70-75°F.

Preheat the Oven: Set your oven to 350°F (180°C) and line two baking sheets with parchment paper.

Prepare the Pumpkin: Spread the Libby's pumpkin puree onto a plate and blot away excess liquid until it feels dry, measuring roughly 1/3 cup.

Whisk Together: In a mixing bowl, combine the cooled brown butter with dark brown sugar and granulated sugar. Whisk for about 1 minute until it resembles wet sand.

Incorporate the Wet Ingredients: Add in the egg yolks, vanilla extract, and the prepped pumpkin puree. Whisk until well combined.

Mix the Dry Ingredients: Gently fold in the all-purpose flour, pumpkin spice, baking soda, cream of tartar, and kosher salt until just combined. Chill if the dough feels too soft.

Make Cinnamon Sugar: In a small bowl, mix together the granulated sugar and ground cinnamon. Roll tablespoon-sized balls of dough in the mixture and place them on the baking sheet.

Bake the Cookies: Bake one tray at a time for 10-12 minutes until edges are golden and centers are puffed and underbaked. Cool completely on a wire rack.