Beat butter and 1/2 cup shortening together until creamy.
Gradually add sugar; beat at medium speed for 5-7 minutes.
Add eggs one at a time, and beat just until the yellow disappears. Combine flour, baking powder, and salt; add to butter mixture alternating with milk; mixing at low speed just until blended after each addition.
Stir in vanilla.
Combine chocolate and 1 tablespoon shortening in a small saucepan and cook over low heat, stirring constantly, until butter melts.
Remove 2 cups batter and add chocolate mixture, stirring until blended. Pour 1/3 of remaining plain batter into the tube pan; top with 1/2 of the chocolate batter.
Repeat layers, ending with a plain batter layer.
Gently swirl with a knife to marble the batter, and sprinkle with pecans.
Bake for 1 hour and 10 minutes, or until a wooden pick inserted in the center comes out clean.
Cool in the pan for 10-15 minutes before removing and allowing to cool completely on a wire rack.