Whisk together boiling water and cocoa. Cover and set aside. With a mixer, cream together the butter, sugar, salt and vanilla extract. Add the eggs, 1 at a time, and continue creaming until light and fluffy. Sift together the flour, baking soda and baking powder and add this mixture, alternately with the buttermilk. Add cocoa and water mixture and mix until thoroughly combined. Scoop into cupcake pans and bake for 20 to 25 minutes.
Let cool completely before decorating.