Follow these step-by-step instructions carefully for perfectly soft, uniform, and delicious whoopie pies. We will first bake the cake shells, then prepare the filling while they cool, and finally assemble our spooky creations.

Part 1: Making the Dark Chocolate Cake Shells

1. Preheat and Prepare: Begin by preheating your oven to 375°F (190°C). Line two large baking sheets with parchment paper. This is a vital step; it prevents the cakes from sticking and ensures easy removal and cleanup.
2. Combine Dry Ingredients: In a medium-sized mixing bowl, whisk together the all-purpose flour, Dutch-processed cocoa powder, baking soda, and salt. Whisking is better than stirring here, as it evenly distributes the leavening agents and aerates the flour, leading to a more consistent rise. Set this bowl aside.
3. Cream Butter and Sugar: In the large bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the softened unsalted butter and granulated sugar together on medium-high speed. Continue creaming for about 3-4 minutes, until the mixture is light in color, fluffy, and has significantly increased in volume. This process incorporates air into the base of your batter.
4. Incorporate Wet Ingredients: Add the room temperature egg and vanilla extract to the creamed butter and sugar. Beat on medium speed until they are fully incorporated, scraping down the sides and bottom of the bowl with a rubber spatula to ensure everything is mixed evenly.
5. Alternate Dry and Wet Mixtures: Turn the mixer speed down to low. Add approximately one-third of the dry ingredient mixture to the bowl, mixing just until the flour streaks disappear. Then, pour in about half of the buttermilk and mix until just combined. Repeat this process: add another third of the dry ingredients, mix, add the remaining buttermilk, mix, and finally add the last of the dry ingredients. Mix only until the last of the flour is incorporated. Over-mixing at this stage can develop the gluten too much, resulting in tough, dense cakes instead of soft, pillowy ones.
6. Scoop the Batter: The batter will be thick and sticky. Using a medium cookie scoop (about 1.5 to 2 tablespoons) is highly recommended for uniform size and shape. Drop rounded mounds of batter onto your prepared baking sheets, leaving about 2 inches of space between each mound as they will spread during baking.
7. Bake to Perfection: Place the baking sheets in the preheated oven and bake for 10-12 minutes. The whoopie pie cakes are done when the tops are set and a gentle press with your fingertip causes them to spring back. Be careful not to overbake, as this will lead to dry cakes.
8. Cool Completely: Remove the baking sheets from the oven and let the cakes cool on the pan for about 5 minutes. Then, carefully transfer them to a wire cooling rack to cool completely. This step is non-negotiable! If the cakes are even slightly warm when you add the filling, the filling will melt and ooze out. This can take at least 30-45 minutes.

Part 2: Preparing the Vibrant Orange Cream Cheese Filling

1. 1. Beat Cream Cheese and Butter: While the cakes are cooling, prepare the filling. In a large, clean mixing bowl, use a hand mixer or a stand mixer with the paddle attachment to beat the softened cream cheese and softened butter together on medium speed until the mixture is completely smooth, creamy, and free of any lumps. This should take about 2-3 minutes.
   2. Add Sugar and Vanilla: Turn the mixer to low speed and gradually add the sifted powdered sugar, one cup at a time. Mixing on low will prevent a sugar cloud from exploding all over your kitchen. Once the sugar is mostly incorporated, add the teaspoon of vanilla extract.
   3. Whip to Fluffy Perfection: Increase the mixer speed to medium-high and whip the filling for another 2-3 minutes. The filling will transform, becoming very light, airy, and fluffy.
   4. Add the Spooky Color: Add a few drops of the orange gel food coloring to the filling. Mix on low speed until the color is evenly distributed. Add more gel, a drop at a time, until you reach your desired shade of vibrant Halloween orange. Remember that gel coloring is very concentrated, so a little goes a long way.

Part 3: Assembling the Halloween Whoopie Pies

1. Pair the Cakes: Once the chocolate cakes are completely cool, arrange them on a clean work surface. Match them up into pairs of similar size and shape.
2. Fill the Pies: Take one cake from a pair and turn it over so the flat bottom side is facing up. Pipe or spoon a generous amount of the orange cream cheese filling onto the center of the cake. A piping bag with a large round tip gives a very clean look, but a spoon or a small offset spatula works just as well.
3. Create the Sandwich: Gently place the second cake of the pair on top of the filling, flat-side-down, and press down lightly until the filling spreads to the edges.
4. Chill and Set: For the best flavor and texture, it’s a great idea to let the assembled whoopie pies chill in the refrigerator for at least 30 minutes before serving. This allows the filling to set up firmly and the flavors to meld together.