In a mixing bowl, combine the melted butter, sugar, and brown sugar, stirring until everything is well mixed.

Add the pumpkin puree to the mixture and stir until fully incorporated.

Next, mix in the egg yolk and vanilla extract until combined.

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

Gradually add the dry ingredients to the wet mixture, stirring until everything is well combined.

Cover the cookie dough with plastic wrap and refrigerate for at least 45 minutes.

While the dough is chilling, preheat your oven to 350°F (175°C) and line a cookie sheet with parchment paper.

Prepare the cinnamon sugar mixture by whisking together ¼ cup of sugar and 2 teaspoons of ground cinnamon in a small bowl.

Once the dough has chilled, scoop it into balls about 1 ½ tablespoons in size.

Roll each ball briefly between your palms to smooth them out, then roll them in the cinnamon sugar mixture.

Place the coated dough balls on the prepared cookie sheet, ensuring they are spaced at least 2 inches apart.

Bake the cookies in the preheated oven for 10-12 minutes.

Keep any remaining dough refrigerated while the cookies are baking, and avoid placing cookie dough on a hot baking sheet.