Preheat oven to 350°F. Spray two 8-inch round cake pans with baking spray, or butter and line the bottoms with parchment paper. If using the butter/parchment method, dust the pans with cocoa powder and shake out the excess.

In a medium bowl, combine the cocoa powder and chocolate chips. Pour the boiling water over them and stir until completely smooth. Set aside to cool slightly.

In the bowl of a stand mixer, combine the sugar, flour, baking powder, baking soda, and salt. Mix on low until combined.

In a small bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla. Add to the flour mixture a little at a time, mixing on low and scraping down the sides as needed.

Slowly add the chocolate mixture and mix until just combined. Scrape the bottom and sides of the bowl to make sure everything is incorporated. The batter will be thin — this is correct.

Divide the batter evenly between the prepared pans. Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean. Start checking at 28 minutes.

Cool the cakes in their pans for 20 minutes, then turn out onto a wire rack and cool completely before frosting — at least 1 hour.

Frost with fluffy white marshmallow icing. For the full frosting recipe, see the Notes section below.