Preheat oven to 375 degrees. Line a baking sheet with parchment paper or nonstick mat; set aside.
In a large bowl, combine the spice cake mix, pumpkin puree, ½ cup softened butter, milk, egg, and pumpkin spice. Use an electric mixer on medium speed to mix together ingredients until smooth.
Using a small (2 tablespoon size) ice cream scoop, drop batter 2 inches apart onto the prepared baking sheet. Dampen hands to lightly smooth out the tops of the dough (optional).
Bake 13-15 minutes or until set. Cool on baking sheet for 5 minutes then cool on wire cooling racks completely. You want the cookies completely cooled before adding the filling.
For the filling, in a medium bowl use an electric mixer to mix together the cream cheese and butter until well combined; about a minute. Add in the powdered sugar and vanilla, and mix until full combined.
For each pie, spread about 1 heaping tablespoon of filling on bottom of a cooled cookie. Top with second cookie, bottom side down, and gently press cookies together.
Notes
Cake Mix: you can find spice cake mix in the boxed cake mix aisle in most grocery stores. Any boxed spice cake mix will work, here I used Duncan Hines. If you can't find spice cake mix, you can use vanilla cake mix instead.
Pumpkin Puree: canned pumpkin puree is available year round. Be sure you are using pure pumpkin puree and not pumpkin pie filling.
Pumpkin Spice: if you can't find pumpkin pie spice, you can use 1 ½ teaspoons of cinnamon and ½ teaspoon of ground nutmeg instead.
Filling: to make this even easier, you can skip making the filling an use a pre-made cream cheese frosting instead.
Storage: store in an airtight container in the refrigerator for up to four days. Bring to room temperature before serving.