Preheat Oven and Prepare Baking Sheets: Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper. Set aside.

Brown the Butter: In a large, light-colored stainless steel saucepan (a light-colored pan makes it easier to see the browning), melt the butter over medium heat. Continue cooking, stirring and swirling the pan occasionally, until the butter is browned and has a nutty aroma. The butter will foam, pop, and crackle – this is normal. Watch carefully to prevent burning. Once the bottom of the pan is covered in brown bits and the butter smells nutty, remove from heat.

Cool Browned Butter: Pour the browned butter (including the browned bits) into a heatproof glass measuring cup. The amount should be slightly under 1 cup (about 184g). Refrigerate the browned butter, stirring every 20 minutes, for about 45-60 minutes, or until it reaches a temperature of 70-75°F (21-24°C). The butter must be cool but still liquid. If it solidifies, let it sit at room temperature for a bit, stirring occasionally, until it’s liquid again.

Dry Pumpkin Puree: Spread the pumpkin puree in a thin layer on a plate. Press a stack of paper towels onto the puree to absorb excess moisture. Scrape the pumpkin into a pile, spread it out again, and repeat the process with fresh paper towels. Continue until the pumpkin puree feels relatively dry and has a texture similar to soft playdough. You should have approximately 1/3 cup (68-75g) of dried pumpkin puree. This step is crucial for preventing overly wet cookies.

Combine Sugars and Butter: Once the browned butter is cool but still liquid, add it to a large mixing bowl. Whisk in the brown sugar and granulated sugar for 1 minute. The mixture should resemble wet sand.

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

Combine Dry Ingredients: In a separate medium bowl, whisk together the all-purpose flour, pumpkin pie spice, baking soda, cream of tartar, and kosher salt.

Combine Wet and Dry: Gradually add the dry ingredients to the wet ingredients, folding with a rubber spatula or wooden spoon until just combined. Do not overmix.

Chill Dough (Briefly): Chill the cookie dough in the refrigerator for 5 minutes to firm it up slightly. If the dough is still very soft after 5 minutes, chill for a few minutes longer.

Prepare Cinnamon-Sugar Mixture: While the dough is chilling, combine the 1/3 cup granulated sugar and 1 teaspoon cinnamon in a small bowl.

Shape and Roll Cookies: Scoop the dough into 3-tablespoon-sized balls (a cookie scoop works well). Roll each dough ball in the cinnamon-sugar mixture until evenly coated.

Arrange on Baking Sheets: Place the coated cookie dough balls on the prepared baking sheets, leaving about 2-3 inches of space between each cookie.

Bake: Bake one tray at a time for 10-12 minutes, or until the edges are golden brown and the centers are puffy and slightly underbaked.

Cool: Let the cookies cool completely on the baking sheets on a wire rack. They will firm up as they cool.