Preheat the oven to 350°F and line two baking sheets with parchment paper.
Start by drying the pumpkin puree. Spread it on a plate and lightly press with a paper towel to absorb excess liquid. Repeat at least four times until the pumpkin reduces from ½ cup to just about ¼ cup. Set aside.
In a small bowl, whisk together the flour, pumpkin pie spice, baking soda, baking powder, and salt. Set aside.
In a large bowl, cream the softened butter and brown sugar together with an electric mixer on high speed for 1-2 minutes until light and fluffy.
Add the egg yolks and vanilla, mixing on medium speed until pale and fluffy, about 1-2 minutes.
Add the dried pumpkin and mix on medium-low speed to combine.
Add the dry ingredients and mix on low speed just until combined.
Scoop the dough with a 2-tablespoon cookie scoop and roll into balls. Then roll the dough balls in the spiced sugar.
- If the dough is too sticky, chill it in the fridge for 10 minutes, then proceed.
Place the cookie dough balls at least 2 inches apart on the baking sheets (bake 6 at a time).
Bake the cookies for 12-14 minutes. For really chewy centers, bake for 12 minutes; for slightly crispier cookies, bake for 14 minutes. The centers will be puffy when done. As they cool, the centers will fall and the cookies will get "wrinkly."
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a cooling rack to finish cooling. They are best enjoyed after cooling for at least 15 minutes!