Blot the pumpkin. Line a medium bowl with two paper towels. Add the pumpkin puree and press another paper towel firmly over the top to absorb excess moisture. After blotting, you should have about 3/4 cup (170g) pumpkin. Set it aside.
Prepare the oven. Preheat the oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats.
Combine the dry ingredients. In a medium bowl, whisk together the rolled oats, flour, baking soda, salt, cinnamon, and pumpkin pie spice.
Cream the butter and sugars. Using a handheld or stand mixer fitted with a paddle attachment, beat the softened butter, granulated sugar, and brown sugar on medium-high speed for about 3 minutes, until light and creamy. Scrape down the sides of the bowl as needed.
Add the wet ingredients. Add the egg yolk and vanilla extract and beat on high speed until combined. Add the blotted pumpkin and beat again until evenly incorporated.
Make the dough. Add the dry ingredients to the pumpkin mixture. Mix on low speed until incorporated, then increase to medium speed and mix until combined. The dough will be soft, creamy, and sticky.
Portion the cookies. Use a medium cookie scoop to portion approximately 1 1/2 tablespoons (25–30g) of dough per cookie. Place the dough balls about 3 inches apart on the prepared baking sheets. Gently flatten each one with the back of a spoon because the cookies will not spread very much on their own.
Bake. Bake for 14–16 minutes, or until the cookies are lightly browned and the edges look set. Let them cool on the baking sheet for 10 minutes, then transfer them to a wire rack to cool completely.
Shape if needed. If any cookies spread unevenly, gently push the edges toward the center with a spoon while they are still warm to create a more rounded shape.
Prepare the filling. Beat the softened cream cheese and butter on high speed for about 1 minute, until smooth and creamy. Add the confectioners' sugar, pumpkin pie spice, vanilla, and salt. Mix on low until incorporated, then beat on high until the filling is smooth and fluffy.
Assemble. Spread or pipe the cream cheese filling onto the flat side of half of the cooled cookies. Place the remaining cookies on top, flat side against the filling, to create sandwiches.
Chill or serve. Serve immediately or cover and store according to the storage instructions below. The finished pumpkin oatmeal cream pies are especially delicious once the filling has had a little time to set.