1. Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.

2. In a bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt until evenly combined.

3. In a separate bowl, cream the softened butter and brown sugar until light and fluffy. Beat in the egg and vanilla extract until smooth.

4. Add the dry ingredients to the butter mixture in thirds, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix just until combined to keep the batter silky. If using, add a little black gel to deepen the cake color.

5. Using a cookie scoop or spoon, drop 24 evenly sized mounds of batter onto the prepared baking sheets, spaced about 2 inches apart.

6. Bake for about 16 minutes, rotating the pans once halfway through baking for even browning. Cakes are set and spring back lightly when done.

7. Cool the cakes completely on the baking sheets for a few minutes, then transfer to wire racks to finish cooling so tops do not become sticky.

8. To make the filling, beat the softened butter and powdered sugar until light and fluffy. Add the vanilla extract and Marshmallow Fluff and beat until smooth and well combined. Tint the filling orange with gel coloring to desired shade.

9. Place the filling in a piping bag. Pipe a generous dollop of filling onto the flat side of 12 cakes, then top with the remaining 12 cakes to form sandwiches. Press gently to spread filling to the edges.

10. Roll the edges of each sandwich in nonpareils to coat the filling rim.

11. Chill the assembled whoopie pies for about 30 minutes to help the filling set. Remove from the refrigerator and rest 15–20 minutes before serving so the cakes soften slightly.