Preheat the oven to 350℉. Line two cookie sheets (13"x18") with parchment paper. Set aside.
In a large mixing bowl using an electric hand mixer, beat the spice cake mix, pure pumpkin, and oil until thoroughly mixed together.
1 box (15.25 oz) spice cake mix, 1 can (15 oz) pure pumpkin, 1/2 cup vegetable oil
Use a medium cookie scoop (1.5 to 2 tablespoons) to scoop out the batter and drop it onto the prepared cookie sheet. Place 12-15 cookies per cookie sheet.*The cookies hardly spread at all while baking so I can fit 15 per cookie sheet. Cook for 9-12 minutes. The cookies should look puffy and when gently pressed with a finger, it should spring right back.
Remove the cookies from the oven and let them cool completely (about 1 hour) before making the whoopie pies.
Add the cheesecake instant pudding mix and heavy whipping cream into a mixing bowl. Use an electric hand mixer to beat until stiff peaks form. Start at low speed and increase the speed as needed.
1 box (3.4 oz) cheesecake instant pudding mix, 2 cups heavy whipping cream
Transfer the whipped cheesecake mixture into a gallon-sized Ziploc bag. Snip the bottom corner off of the bag, and pipe a generous amount onto one cookie, and then gently place another cookie on top of it to create the whoopie pie sandwich cookie.
These can be served immediately OR for the best flavor I recommend refrigerating the prepared whoopie pies for at least 2-4 hours before serving. Keep leftovers stored in an airtight container, in the fridge, for up to 7 days.