Whisk the dry ingredients: Combine oats, flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice.
Cream the butter and sugars: Beat until light and fluffy, then mix in pumpkin, egg yolk, and vanilla.
Combine the mixtures: Add the dry ingredients in two batches, mixing until just combined. Fold in the dried cranberries.
Chill the dough: Refrigerate for at least 1 hour (overnight for best flavor).
Scoop and roll: Measure 1½ tablespoons of dough per cookie, roll into balls, and chill again for 15–20 minutes.
Bake: Bake at 350°F for 10–12 minutes, until the edges are lightly golden. Tap the pan on the counter to flatten slightly, then cool completely.
Make the filling: Beat butter and cream cheese until smooth. Gradually add powdered sugar, vanilla, and salt; mix until fluffy.
Assemble the sandwiches: Pipe or spread filling on the bottom of half the cookies. Top with remaining cookies and press gently.
Notes
*Blotting the pumpkin: Getting rid of extra liquid in the pumpkin puree keeps the cookies from becoming too cakey. Blotting the pumpkin helps them bake up with the right cookie consistency: crispy around the edges and chewy in the center. To do this, spread the puree onto a small plate and place a folded paper towel over the top, pressing gently so it absorbs the moisture. Repeat about 4-5 more times, using a new paper towel each time.