Step 1: Prepare the Dough

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
2. Mix Dry Ingredients: In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
3. Cream Butter and Sugars: In a large mixing bowl, use a hand mixer or stand mixer to cream the softened butter, granulated sugar, and brown sugar together until light and fluffy, about 2-3 minutes.
4. Add Wet Ingredients: Beat in the egg, vanilla extract, vinegar, and red food coloring. Mix until fully combined, ensuring the color is evenly distributed.
5. Incorporate Dry Ingredients and Buttermilk: Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. Start and end with the dry ingredients, mixing just until combined. Avoid overmixing to maintain a tender texture.

Step 2: Bake the Cookies

6. Scoop and Shape: Use a small cookie scoop (about 1 ½ tablespoons) to portion the dough onto the prepared baking sheets, spacing them 2 inches apart.
7. Bake: Bake the cookies for 10-12 minutes, or until the edges are set and the tops spring back when lightly touched. Avoid overbaking for soft, cake-like cookies.
8. Cool: Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.

Step 3: Prepare the Cream Cheese Filling

9. Beat the Cream Cheese and Butter: In a mixing bowl, beat the softened cream cheese and butter together until smooth and creamy.
10. Add Powdered Sugar and Vanilla: Gradually add the sifted powdered sugar, ½ cup at a time, mixing on low speed to avoid a sugar cloud. Stir in the vanilla extract and beat on medium speed until fluffy.

Step 4: Assemble the Whoopie Pies

11. Match Cookies: Pair up the cookies by size for a uniform look.
12. Fill: Pipe or spread about 1 ½ tablespoons of cream cheese filling onto the flat side of one cookie. Top with a matching cookie, pressing gently to create a sandwich.
13. Chill: For best results, chill the assembled whoopie pies in the refrigerator for 20-30 minutes to set the filling.