Combine butter, sugar, and brown sugar and stir until well-combined. Add pumpkin and stir well.

Stir in egg yolk and vanilla extract.

In a separate bowl, whisk together flour, pumpkin spice, baking soda, cream of tartar, and salt until well-combined.

Gradually add dry ingredients to wet until ingredients are well-combined.

Cover cookie dough with clear wrap and place in the refrigerator to chill for at least 45 minutes.

Preheat oven to 350?F (175?C) and prepare a cookie sheet by lining with parchment paper. Prepare the cinnamon sugar mixture by whisking together ? cup sugar and 2 teaspoons ground cinnamon in a small bowl.

Remove dough from refrigerator and scoop into 1 ? Tablespoon-sized balls. Roll briefly between your palms until smooth and then roll through cinnamon sugar and transfer to prepared cookie sheet, spacing at least 2 inches apart.

Bake cookies in a 350?F oven for 10-12 minutes. Keep remaining dough refrigerated while cookies are baking and do not place cookie dough on a hot baking sheet.

Allow baked cookies to cool completely on the cookie sheet before enjoying.