Prep and line: preheat your oven to 375°F and line two baking sheets with parchment paper.
Combine flour, leaveners, spices, and salt: combine the flour, baking powder, baking soda, spices, and salt in a small bowl and stir until well combined. Set aside.
Combine the wet ingredients: stir together the pumpkin puree, eggs, buttermilk, maple syrup, and vanilla extract until well combined. Set aside.
Cream butter and sugars: cream butter and both sugars using a hand or stand mixer for 2-3 minutes on medium-high until light and fluffy. (We're working with alot of batter throughout this recipe, so make sure you are regularly scraping the bowl well throughout the mix steps).
Add in the wet + dry ingredients: add in the pumpkin mixture and flour mixture, and mix on medium speed for about 1 minute until all ingredients are fully combined and batter is smooth.
Scoop and tray: scoop batter, using 2 tablespoons of batter per cookie (an ice-cream scoop works well here for easy portioning and shaping!), and drop in rounds on prepared baking sheets at least 2” apart.
Bake: bake for 9-12 minutes, just until tops are fully set, lose their shine, and spring back when gently pressed. The bottoms should be browned as well.
Cool: allow cookies to fully cool while you prepare the frosting.
TO MAKE THE FROSTING:
Beat together all ingredients: place all frosting ingredients in a medium sized bowl. Beat on low speed using a hand or stand mixer, just until the ingredients are roughly combined, and then 30 seconds on medium speed until smooth and fully combined.
TO ASSEMBLE THE WHOOPIE PIES:
Marry the whoopies: pair cookies according to the best matches by size and dimension on your work surface or a baking sheet with the flat bottoms facing up.
Fill with frosting: using a pastry bag, or a spoon/ice cream scoop and a dinner knife, top one cookie in each pair with 1-2 tablespoons of frosting each. Spread frosting into an even layer until it's just shy of the edge (if piping into a neat, even layer, you don't need to spread it out any further).
Sandwich and enjoy! Top the frosted cookie with it's matching cookie to make a sandwich, and gently press the cookies together until the filling reaches the edge of the cookies. Pass those mini sandwiches of joy around the room and listen to everyone holler "whoopie" when they take their first bite!
*1Spice blends: if you’re in a hurry or just don’t have the individual spices at home, you can start with 2 ½ teaspoons of pre-made pumpkin pie spice in your cookies in place of all the individual spices, and then add more to taste if you like.
*2Pumpkin Puree not Pie Filling: make sure you get 100% pumpkin puree, not pumpkin pie filling which has sugar and other additives. They look very similar at the store and can be easy to mix up, so just be sure to double-check your label!
*3Buttermilk or milk? The base of these whoopies is pretty sweet to counteract the vegetal notes of all the pumpkin puree, so I prefer buttermilk's acidity to balance that sweetness out a bit. But if you only have regular milk at home, that'll work fine too!
A Whole Lot O’ Whoopies: this recipe makes a lot of mini whoopie pies as I find there are never enough to go around. But if 30 is too many for you, just use the toggle at the top of the ingredients section in the recipe card to resize to a half-batch which is about 15 mini whoopie pies.
Storage: store airtight in the fridge for up to 5 days, or at room temperature for up to 2 days.