Combine melted, cooled butter and sugars in a large bowl and stir well.

Add pumpkin, egg yolk, and vanilla extract and stir to combine.

In a separate, medium-sized bowl, whisk together flour, baking powder, baking soda, salt, and pumpkin spice until well-mixed.

Gradually add dry ingredients to wet (I do this in 3-4 parts) stirring until ingredients are thoroughly combined.

Cover bowl and chill in the refrigerator for at least 60 minutes.

Once dough has nearly finished chilling, preheat oven to 350F (175C) and prepare cookie sheet by lining with parchment paper.

Once oven is preheated, remove dough from the fridge and scoop by 1 ½ Tablespoon-sized scoops. If desired, roll into a smooth round ball.

Bake on 350F (175C) for 13-15 minutes and allow to cool completely on baking sheet before adding glaze (if using).

Glaze: In a medium-sized bowl whisk together powdered sugar, milk, corn syrup, and vanilla extract until smooth and the drizzle that falls from the whisk holds its shape for a second before dissolving into the bowl. If icing is too stiff, add a teaspoon more milk at a time, if it is too thin add a Tablespoon more powdered sugar at a time.

Hold completely cooled cookie firmly by the base and dip the surface directly into the glaze (alternatively you can just use a spoon to drizzle the glaze over the cookies). Return to cookie sheet or cooling rack to allow the glaze to harden (about 30-60 minutes) before enjoying.