In a saucepan, brown the unsalted butter over medium heat until golden and nutty, about 5-7 minutes. Transfer to a mixing bowl and cool for 10 minutes.

Add pumpkin puree, granulated sugar, brown sugar, egg yolk, and vanilla extract to the cooled butter. Mix well.

In a separate bowl, whisk together the all-purpose flour, baking soda, cream of tartar, pumpkin pie spice, and salt.

Gradually mix the dry ingredients into the wet ingredients until a soft dough forms. Cover and refrigerate for 30-45 minutes.

Preheat the oven to 350°F (175°C). Mix granulated sugar and cinnamon in a small bowl.

Scoop tablespoon-sized portions of dough, roll into balls, coat in the cinnamon-sugar mixture, and place on a parchment-lined baking sheet.

Bake for 10-12 minutes until edges are set and tops are crackled. Cool on the sheet for 5 minutes before transferring to a rack.