Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper. Spread the 1/3 cup of pumpkin puree onto a double layer of paper towels and press another paper towel on top to blot out excess moisture until reduced to a thick 1/4 cup.

In a large bowl, whisk the warm browned butter, dark brown sugar, and granulated sugar for 60 seconds until glossy. Whisk in the blotted pumpkin puree, egg yolk, and vanilla extract until smooth.

Fold in the flour, pumpkin pie spice, cream of tartar, baking soda, and salt with a spatula until a soft, non-sticky dough forms.

Stir the 1/3 cup granulated sugar and 1 1/2 teaspoons cinnamon together in a shallow bowl. Scoop 1.5- to 2-tablespoon balls of dough, roll between your palms, and coat generously in the cinnamon sugar.

Arrange 2 inches apart on the prepared baking sheets and bake for 9–11 minutes until the edges are set and the tops are puffed and crinkly. Cool on the pan for 5 minutes so the centers set into fudgy perfection.