Make the Whoopie Pies: Melt the butter in a large mixing bowl. Whisk in the oil, then the sugars. Add eggs, pumpkin, and vanilla and whisk until well combined and smooth. Add the dry ingredients and fold in with a silicone spatula until just incorporated. The batter will be a tad lumpy and slightly thick. Don't over mix!
1/4 cup salted butter, melted, 3/4 cup vegetable oil, 2 cups brown sugar, packed, 3 tbsp granulated sugar, 2 large eggs, at room temperature , 2 and 3/4 cups canned pumpkin, 2 tsp vanilla extract, 3 cups all-purpose flour, spooned & leveled or weighed, 1/2 tsp salt, 1 tsp baking powder, 1 tsp baking soda, 2 and 1/4 tsp cinnamon, 1 and 1/4 tsp ginger, 1 tsp nutmeg, 1/2 tsp ground cloves
Make the Frosting: Once the butter has cooled, beat it together with the softened cream cheese in a medium mixing bowl. It will seem lumpy at first but just keep mixing until it smooths out. Mix in the powdered sugar in two additions. Add the maple syrup, milk, and cinnamon and mix until well combined. Taste and adjust as desired.
6 oz cream cheese, 3 cups powdered sugar, adjust to taste, 1/4 tsp cinnamon, 1 tbsp maple syrup, 1 tsp vanilla extract