Prepare the oven and baking sheets. Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.
Make the coating. In a small bowl, combine the granulated sugar and ½ teaspoon pumpkin pie spice. Set aside.
Drain the pumpkin. Place the pumpkin purée in a clean kitchen towel or cheesecloth and squeeze thoroughly to remove excess moisture.
Mix the dry ingredients. In a medium bowl, whisk together the flour, pumpkin pie spice, baking soda, baking powder, salt, and cornstarch.
Cream the butter and sugar. In a large bowl, beat the softened butter and light brown sugar until creamy. Add the egg yolks, vanilla, and drained pumpkin purée. Mix until evenly combined, scraping down the bowl as needed.
Finish the dough. Add the dry ingredients and mix on low speed just until incorporated. Use a spatula to bring in any flour remaining at the bottom of the bowl.
Shape and coat. Portion the dough with a small cookie scoop and roll it between your hands into balls. Roll each ball in the spiced sugar mixture.
Arrange on the baking sheets. Leave about 3 inches (7.5 cm) between the dough balls because the cookies spread considerably. Bake in batches as needed.
Bake. Bake for 12–15 minutes, until the edges are set and the centers still look slightly soft. Begin checking at 12 minutes.
Cool. Let the cookies cool on the baking sheet before moving or serving. Allow the baking sheet to cool before adding another batch of dough.
