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.
One dough is nearly finished chilling, preheat oven to 350F (175C) and prepare a cookie sheet by lining with parchment paper. Prepare your cinnamon sugar mixture by whisking together 1/4 cup sugar and 2 tsp ground cinnamon in a small bowl.
Remove dough from refrigerator and scoop into 1 1/2 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" apart.
Bake cookies in a 350F oven for 10-12 minutes. Keep your 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 cookie sheet before enjoying.