Preheat your oven to 350°F and line a baking sheet with parchment paper or silicone baking mat.
In a small, microwave-safe bowl, microwave butter for 20 to 30 seconds, until mostly melted. Set aside to cool.
In a small bowl, whisk together flour, baking soda, salt, and spices. Set aside.
In a medium bowl, combine melted butter, granulated sugar, and brown sugar, and whisk until well-combined. Add egg yolk, canned pumpkin, and vanilla extract and whisk until smooth.
Use a spoon to stir in flour mixture until just combined. Scoop 1 1/2-ounce scoops of dough (this should make 8 cookies) and place on a cookie sheet (for the roundest cookies, roll your dough into a ball before placing on the sheet). Use the palm of your hand to smash the dough to 1/2-inch thickness.
Bake for 8 to 11 minutes, until the tops of the cookies look set and the bottoms are just slightly browned. Cool completely before frosting.