Preheat oven to 350°F. Line two baking sheets with parchment paper and set out 1 large cooling rack.
In the bowl of a stand mixer fitted with the whisk attachment, add butter and sugars and mix on low speed until thoroughly combined. Add eggs, one at a time, mixing as you go. Once mixture is smooth, add sweet potatoes and thoroughly combine.
In a separate mixing bowl, combine flour, baking soda and powder, salt and spices. In three batches, alternate adding flour mixture and heavy cream to wet mixture. Using a rubber spatula, scrape bottom and sides of bowl with wet ingredients as you go.
Using a 3-tablespoon ice cream scoop, scoop batter onto baking sheets, evenly spaced apart. Bake for 18 to 20 minutes. Remove to cooling rack and allow to cool completely.
Filling
In the bowl of a stand mixer fitted with the paddle attachment, beat butter on low speed for 6 minutes. Add marshmallow topping and maple syrup and mix until thoroughly combined. Add powdered sugar and milk in alternating batches and mix until well combined.
Pipe or dollop filling onto the bottom of one cookie, then top with another cookie to form whoopie pies. Repeat with remaining cookies and filling. Serve.
Notes
- Marshmallow: You can use actual toasted marshmallows here or fluff.- Pies: You can also make the cookies by themselves if you prefer.