In a large bowl, cream together butter and brown sugar until light and fluffy.
Beat in egg yolk and vanilla.
In a separate bowl, whisk together flour, baking powder, cinnamon, nutmeg, and salt.
Add dry ingredients to wet ingredients and mix until just combined.
If the dough feels crumbly, add milk or cream 1 tsp at a time until it comes together.
Divide dough into two discs, wrap in plastic wrap, and chill for at least 2–4 hours (or overnight) until firm enough to roll.
In a small bowl, whisk pumpkin purée, brown sugar, pumpkin pie spice, egg yolk, cream, and vanilla until smooth.
Cover and refrigerate until ready to use.
Preheat the oven to 350°F. Line two baking sheets with parchment paper.
On a lightly floured surface (or between sheets of wax paper), roll chilled dough to about ¼ inch thickness.
Use a larger cookie cutter (e.g., 3–3.5 inch fluted circle) to cut an even number of shapes.
For half of those cutouts, use a smaller cutter (e.g., 2 inch circle) to remove the centers—these will be the “tops.”
Transfer all cutouts to prepared baking sheets.
Chill for 10–15 minutes to help keep their shape.
Place the solid “base” cookies on the sheet.
Spoon or pipe 1–1½ tsp pumpkin filling into the center of each base, spreading slightly but leaving a small border.
Gently place the “top” cookies (with holes) over the filling, pressing lightly to adhere but not squish the filling out.
Bake for 11–14 minutes, or until the edges are lightly golden. The tops should remain pale for a “pie crust” look.
Cool completely on a wire rack.
If desired, pipe or dollop whipped cream into the filling hole once cooled.