Cake Preparation: Cream the butter and gradually add the brown sugar, beating well until fluffy and well combined. Add the eggs, one at a time, beating well after each addition. Add the chocolate, mixing well.
Comine the flour, salt and baking soda. Gradually add the flour to the chocolate mixture alternately with sour cream, beating well after each addition. Add water, mixing well. Stir in the vanilla. This mixture will be thin. Pour the batter evenly into two greased and floured 9 inch cake pans. Bake at 350 degrees F. for 45 minutes. Let pans cool about 10 minutes before removing the cake from the pans.
Frosting Preparation: Combine the chocolate and butter over low heat until melted, stirring constantly. Combine the sugar, milk and vanilla in a medium mixing bowl. Set the bowl in a pan of ice water and stir in the chocolate mixture. Beat for 2 minutes at a high speed on electric mixer until the icing is the proper spreading consistency.