Microwave chocolate in a 1-quart microwave-safe bowl at HIGH 1 1/2 minutes, stirring twice.
Beat butter and shortening at medium speed with an electric mixer until creamy; gradually add sugar, beating well. Add eggs, 1 at a time, beating until blended after each addition. Stir in melted chocolate.
Combine flour, baking powder, and salt; add to butter mixture, alternately with milk, beginning and ending with flour mixture. Stir in extracts. Fold in chopped pecans, if desired. Pour into a greased and floured 10-inch tube pan.
Bake at 300° for 1 hour and 30 to 45 minutes or until a wooden pick inserted in center of cake comes out clean. Cool in pan on a wire rack 10 minutes; remove from pan, and cool completely on wire rack. Spread top and sides of cake with Chocolate Frosting.