Preheat oven to 350F. Grease 2 8-inch layer cake pans well, then dust them generously with cocoa. (This gives the cake layers a rich brown finish). Sift the flour, cocoa, baking soda and salt onto a piece of waxed paper and set it aside.
Cream the butter until it is fluffy, add the sugar and vanilla, and continue beating until the batter is silvery and light. Beat the eggs in one by one, then add the sifted dry ingredients, alternately with the boiling water, beginning and ending with the dry ingredients and beating well after each addition.
Divide the batter equally between the two pans, smoothing the tops. Bake the layers uncovered for 30 to 35 minutes, or until the layers feel spongy to the touch and begin to pull away from the sides of the pans. Cool the layers upright in their pans on wire racks for 10 minutes, then carefully loosen them around the edges with a spatula and turn them onto wire racks. Cool them completely.
Frosting: Cream the butter until it is light, then add the confectioners sugar gradually, beating all the while. Beat in the melted chocolate and vanilla, then add just enough cream to make the frosting a good consistency for spreading. Sandwich the two cake layers together with frosting, then frost the top and sides of the cake. Swirl the frosting into peaks and valleys.