In a medium mixing bowl beat cream cheese, 1/3 cup butter or margarine, and shortening with an electric mixer on medium to high speed for 30 seconds. Add brown sugar, egg, and 1/2 teaspoon vanilla. Beat until thoroughly combined. Beat in flour and baking soda on low speed just until combined. Stir in the chopped chocolate.
Spread cookie dough evenly in a greased 12- or 13-inch pizza pan. Bake in a 350 degree F oven for 20 to 22 minutes or until lightly browned around the edges.
Meanwhile, for the fudgy frosting, in a small mixing bowl combine powdered sugar, unsweetened cocoa powder, 1/4 cup softened butter or margarine, boiling water, and 1/2 teaspoon vanilla. Beat with an electric mixer on low to medium speed until combined. Beat on medium speed about 1 minute or until fluffy.
Frost with Fudgy Frosting. Sprinkle with chopped nuts. Cut into wedges. Makes 12 servings.