Spread pumpkin puree between folded paper towels and blot several times until thick and matte. You should have about 3 tablespoons (45–50g) blotted pumpkin.

Melt butter in a light-colored saucepan over medium heat, stirring or swirling frequently. Cook for 4–6 minutes, until the milk solids turn deep golden brown and smell nutty. Pour into a mixing bowl and cool for 10–15 minutes.

Whisk brown sugar and granulated sugar into the brown butter. Add blotted pumpkin, egg yolk, and vanilla and whisk until smooth.

In a separate bowl, whisk flour, cream of tartar, baking soda, cinnamon, pumpkin pie spice, and salt. Fold into the pumpkin mixture just until no dry flour remains. Cover and refrigerate for 45–60 minutes.

Preheat oven to 350°F (177°C) and line baking sheets with parchment. Mix the coating sugar, cinnamon, and salt in a shallow bowl.

Scoop dough into 2-tablespoon (about 35g) portions, roll into balls, then generously coat in cinnamon sugar. Arrange at least 2½ inches apart on the prepared baking sheets.

Bake one sheet at a time for 11–13 minutes, until the edges are set and the tops are puffed and cracked but the centers still look slightly soft. Cool on the baking sheet for 10 minutes, then transfer to a wire rack.