Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper.

In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth.

Stir in the pumpkin puree, egg yolk, and vanilla extract until fully combined.

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

Gradually add the dry ingredients to the wet ingredients, mixing just until a soft dough forms.

Cover and refrigerate the dough for at least 1 hour.

In a small bowl, stir together the granulated sugar and cinnamon for the coating.

Scoop the chilled dough into 1½-tablespoon portions and roll each into a ball.

Roll each dough ball in the cinnamon sugar mixture until completely coated.

Place the cookies 2 inches apart on the prepared baking sheets.

Bake for 10 to 12 minutes, or until the edges are set and the centers still appear slightly soft.

Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.