Preheat oven to 350°F. Line two cookie sheets with parchment paper or spray with cooking spray.
In a large bowl, add the cake mix, butter, pumpkin, eggs, and pumpkin pie spice. Mix slowly for 30 seconds or until combined, then beat for 1-2 minutes. Batter will be on the wet side.
Drop tablespoon-sized dollops onto the cookie sheet. Try to make sure that they are all the same size.
Bake one pan at a time for 10-11 minutes. Let them cool completely.
To make the frosting: Combine the cream cheese and butter in a medium bowl with an electric mixer until smooth. Add the powdered sugar and mix at low speed until combined. Stir in the vanilla and mix again for a few minutes until light and fluffy. You may need to add a little milk or cream to make it spreadable if your butter wasn't soft enough.
Frost a cookie with a dollop of cream cheese frosting and top with another cookie. Store in an airtight container and refrigerate. Make 30 whoopie pies.