Make the Dough: In a stand mixer fitted with a paddle attachment, cream together butter and brown sugar until light and fluffy (about 2 minutes). Add egg yolks and vanilla, mixing until smooth.
In a separate bowl, whisk together the flour, baking powder, and salt. Slowly add to the wet ingredients and mix on low until a soft dough forms. If the dough feels sticky, chill it for 20–30 minutes.
Preheat + Shape: Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
Roll dough into 1-inch balls, then roll each in cinnamon sugar. Place on prepared sheets, spaced about 2 inches apart.
Use your thumb or the back of a ½ teaspoon to press a deep well into the center of each ball.
Make the Filling: Whisk together pumpkin puree, egg yolks, brown sugar, cream, cornstarch, pumpkin pie spice, salt, and vanilla in a medium bowl until smooth.
Fill + Bake : Spoon or pipe about 1 teaspoon of filling into each warm cookie well. Bake for 11-12 minutes, or until filling is matte.
Cool + Finish: Let cookies cool on the baking sheet for 10 minutes before transferring to a wire rack. The centers will firm up as they cool.
Optional: Pip cooled cookies with cream cheese frosting or dust with extra cinnamon sugar before serving.