Preheat oven to 350°. Butter and flour a 13x9x2-inch baking pan.
Cream shortening with sugar until light. Add egg yolks and beat until fluffy. Sift together the sifted cake flour, 2 teaspoons baking powder, salt, and spices. Add the orange peel to dry mixture. Add milk to creamed mixture alternately with the dry ingredients. Stir in the melted chocolate until well blended. Beat egg whites until stiff peaks form; fold into the batter. Pour into a 13x9x2-inch baking pan and bake at 350° for 40 to 50 minutes.
Frost with a buttercream or cream cheese frosting, top a dessert sauce, or dust with confectioners' sugar before serving.
Calories per serving: 391
Fat per serving: 16.4g