Get ready. Preheat your oven to 350°F and line a baking sheet with parchment paper. Mix your cinnamon sugar coating ingredients in a bowl and set aside.
Brown that butter. In a small saucepan over medium heat, melt the butter and keep stirring until it turns golden brown and smells nutty. You'll see little brown bits at the bottom—that's the good stuff. Let it cool slightly.
Dry the pumpkin. This step is crucial. Spread your pumpkin puree on thick paper towels, wrap it up, and squeeze out every bit of moisture you can. We want concentrated pumpkin flavor, not soggy cookies.
Make the dough. In a large bowl, whisk together the brown butter, dried pumpkin puree, and both sugars until combined. Add the egg yolk and vanilla, mixing well. Then add the flour, baking soda, cream of tartar, salt, and all the spices. Mix until you have a soft dough with no flour streaks.
Coat and bake. Use a cookie scoop to portion out the dough, roll each ball thoroughly in the cinnamon sugar mixture, and place them 2 inches apart on your prepared baking sheet. Bake for 10-12 minutes until they're puffed and set around the edges but still look slightly underdone in the centers.
Practice patience. Let them cool on the pan for a few minutes before transferring to a wire rack. This is the hardest part, but warm cookies fall apart easily.
