In a bowl, combine chocolate and water; stir until blended. Cool. Add the sugar, shortening, egg and vanilla; mix well. Combine the flour, baking soda and salt; gradually add to the chocolate mixture alternately with buttermilk. Pour into a greased 8-in. square baking dish.
Bake at 350° for 30-35 minutes or until a toothpick inserted in the center comes out clean. Cool completely.
For frosting, combine the first six ingredients in a saucepan; bring to a boil. Boil for 1-1/2 minutes; remove from the heat. Set pan into a large pan of ice water. Beat for 1 minute. Add butter and vanilla. Beat 10 minutes longer or until frosting achieves spreading consistency. Frost cake. Yield: 4 servings.