How to Make It
Beat butter and 1/2 cup shortening at medium speed with an electric mixer about 2 minutes or until creamy. Gradually add sugar, beating at medium speed 5 to 7 minutes. Add eggs, one at a time, beating just until yellow disappears.
Combine flour, baking powder, and salt; add to butter mixture alternating with milk, beginning and ending with flour mixture. Mix at low speed just until blended after each addition. Stir in vanilla.
Combine chocolate and 1 tablespoon shortening in a small, beavy saucepan; cook over low heat, stirring constantly, until chocolate melts. Remove 2 cups batter, and add chocolate mixture, stirring until blended. Pour one-third of remaining plain batter into a greased and floured 10-inch tube pan; top with half of chocolate batter. Repeat layers, ending with plain batter.
Gently swirl batter with a knife to create a marbled effect, and sprinkle with pecans. Bake at 350° for 1 hour and 10 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 to 15 minutes; remove from pan, and let cool completely on wire rack.