Blot the pumpkin: Line a medium bowl with 2 paper towels. Place the pumpkin puree in the bowl. Using another paper towel, press down to blot excess moisture out of the pumpkin. After blotting, make sure you have about 3/4 cup (170g) of pumpkin. Discard paper towels and set blotted pumpkin aside.
Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside.
In a medium bowl, whisk the oats, flour, baking soda, salt, cinnamon, and pumpkin pie spice together.
In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter and both sugars together on medium-high speed until creamed, about 3 minutes. Scrape down the sides of the bowl as needed. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the egg yolk and vanilla extract and beat on high speed until combined. Add the blotted pumpkin, and beat on high speed until combined. Add the dry ingredients to the wet ingredients and mix on low speed until incorporated, then increase to medium speed and beat until combined. Dough will be creamy, soft, and sticky.
Using a medium cookie scoop, scoop cookie dough (about a scant 1 and 1/2 Tablespoons (25–30g) of dough each) and drop on the cookie sheet, about 3 inches apart. With the back of a spoon, press down to slightly flatten the balls, as the cookies won’t spread much unless you help out first. Bake for 14–16 minutes or until lightly browned and set on the edges. Remove from the oven and allow cookies to cool for 10 minutes on the baking sheet, then transfer to a cooling rack to cool completely. (Success Tip: If your cookies are spreading unevenly, remove them from the oven and use a spoon to lightly push any wonky edges back in towards the center, to reshape into circles. You can repeat this trick again, if needed, when you take them out of the oven after baking.) Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat cream cheese and butter on high speed until smooth and creamy, about 1 minute. Add the confectioners’ sugar, pumpkin pie spice, vanilla, and salt. Beat on low speed until confectioners’ sugar is incorporated, then increase to high speed and beat until smooth and creamy. Pipe or spread some of the filling on the bottom side of half of the cooled cookies; top with remaining cookies, right side up. I used Wilton 2A tip to pipe. Cover and store leftover cookies at room temperature for up to 1 day. After that, store in the refrigerator for up to 1 week to keep the creamy filling fresh.
