Preheat oven to 350°F. Spray cupcake pans with nonstick cooking spray or line with cupcake liners and set aside.
In a medium bowl, whisk the flour, cocoa powder, sugar, baking soda, baking powder, and salt together. Set aside.
1¾ cups all-purpose flour, ¾ cup unsweetened cocoa powder, 2 cups granulated sugar, 1½ teaspoons baking soda, 1½ teaspoons baking powder, 1 teaspoon kosher salt
In a large heatproof bowl, whisk the buttermilk, eggs, vanilla, and melted butter together.
1 cup buttermilk, 2 large eggs, 2 teaspoons pure vanilla extract, ½ cup salted butter
Combine the wet and dry ingredients and beat together with a hand mixer or by hand with a whisk. Gradually add in the boiling water while mixing to help break apart the batter. Batter will be thin.
1 cup water
Pour the batter into the prepared muffin tins (filling about 3⁄4 of the way full).
Bake for 22-25 minutes or until a toothpick inserted into the cakes comes out with just a few crumbs.
Cool cupcakes completely.
Meanwhile, prepare the frosting.
Chocolate buttercream frosting
Top the cooled cupcakes with buttercream.