Directions

1. Preheat oven to 350 degrees. Butter two 4-inch muffin top pans. Line each muffin cup in the pan with a parchment paper round, butter parchment, and set aside.
2. Cream together butter and sugar in the bowl of an electric mixer fitted with the paddle attachment until combined, 2 to 3 minutes. Add salt, eggs, and vanilla, and beat just until combined.
3. In a small bowl, mix together baking soda and buttermilk. Add flour to mixer, alternating with buttermilk mixture, beginning and ending with flour.
4. In a medium bowl, whisk together cocoa powder and boiling water until smooth. Add to batter and beat until combined.
5. Fill each muffin cup with a heaping 1/4 cup batter. Transfer muffin pans to oven and bake 9 minutes, rotate pans, and continue baking 9 minutes more. Let cool slightly before transferring muffin tops to a wire rack. Let cool completely; remove parchment paper. Repeat process with remaining batter.
6. Place a heaping 1/4 cup filling on the bottom side of half of the muffin tops. Top with remaining muffin tops, bottom side down, to form whoopie pies.