• Preheat the oven to 350°F. Line two large baking sheets with parchment paper.
• In a large mixing bowl, beat the softened butter, granulated sugar, and light brown sugar until smooth and creamy, about 1–2 minutes.
• Beat in the egg and vanilla until fully combined.
• Add the flour, cornstarch, baking powder, baking soda, cinnamon, and salt. Mix just until a thick, soft cookie dough forms.
• Using a medium cookie scoop, portion the dough into balls, about 1½ tablespoons each. You should get approximately 16 cookies.
• Place the dough balls on the prepared baking sheets and refrigerate for 30 minutes.

Make the Filling

• While the dough chills, make the pumpkin filling. In a medium bowl, whisk together the pumpkin puree, granulated sugar, egg yolk, heavy cream, vanilla, cinnamon, pumpkin pie spice, and cornstarch until smooth and creamy.
• Remove the chilled dough balls from the refrigerator.
• Use the back of a 1-tablespoon measuring spoon to press a well into the center of each dough ball. Press down firmly enough to create room for the filling, but do not flatten the entire cookie. Leave a thick raised border around the outside.
• Spoon the pumpkin filling into each well, filling it nearly to the top without overflowing onto the cookie border.
• Bake for 14–16 minutes, or until the cookie edges are set and very lightly golden and the pumpkin filling looks set.
• Let the cookies cool on the baking sheet for about 10 minutes, then carefully transfer them to a wire rack to cool completely.
• Once completely cool, top each cookie with a small swirl of whipped topping and a light dusting of cinnamon or pumpkin pie spice, if desired.