Make the Cookies:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
2. Mix Dry Ingredients: In a medium bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt.
3. Cream Butter and Sugar: In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
4. Add Egg and Vanilla: Beat in the egg and vanilla extract until well combined.
5. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, alternating with the milk, mixing until just combined.
6. Scoop the Batter: Use a cookie scoop to drop tablespoon-sized mounds of batter onto the prepared baking sheets, leaving space between each mound.

Bake the Cookies:

7. Bake: Bake for 10-12 minutes, or until the edges are set. Remove from the oven and let cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.

Make the Filling:

8. Beat the Butter: In a large bowl, beat the softened butter until creamy.
9. Add Sugar and Cream: Gradually add the powdered sugar, mixing on low until combined. Add the heavy cream and vanilla extract, then beat on high until fluffy.
10. Color the Filling: If desired, mix in orange food coloring until you reach the desired shade.

Assemble the Whoopie Pies:

11. Fill the Cookies: Once the cookies are completely cool, spread a generous amount of filling on the flat side of one cookie, then top with another cookie, flat side down.
12. Decorate: Roll the edges in Halloween-themed sprinkles and add edible candy eyes on top for a fun look. You can also use fondant to create spooky designs.