I did not come up with this recipe myself. I got this recipe from a magazine and tried it the first time for my first husbands birthday which was three days before Halloween. Everyone loved it and I made it ever since for Birthday's, Anniversaries or just because it is so delicious.
In a saucepan, combine the water, butter, shortening and cocoa; cook and stir until butter and shortening are melted. In a large bowl, combine the flour, sugar, baking soda and salt. Add the butter mixture; mix well. Add the eggs, buttermilk and vanilla; mix well.
Pour into a greased and waxed paper-lined 15-in. x 10-in. x 1-in. baking pan. Bake at 350° for 20-25 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack to cool completely. Gently peel off waxed paper. Transfer to a 17-in. x 12-in. covered board.
In a saucepan, heat the cream until bubbles begin to form around sides of pan. Remove from the heat; stir in chocolate chips until melted. Place pan in a bowl of ice water; stir constantly until cooled. Gradually whisk in enough confectioners' sugar to achieve spreading consistency. Frost the top and sides of cake.
In a small bowl, cream the butter and shortening. Beat in confectioners' sugar, milk and vanilla until smooth. Place 1/3 cup in a small bowl; tint orange. Place 3 tablespoons in another bowl; tint purple.
Trace a ghost pattern. Cut out with a shape knife, trace the ghost on chocolate frosting. Gently spread white frosting in ghost shape. Place orange frosting in a pastry or plastic bag; cut a hole in one corner. Pipe banner on ghost. Cut a hole in corner of another pastry or plastic bag; insert #2 round pastry tip and purple frosting. Pipe "Happy Boo-Day" on banner.