- Beat butter at medium speed with an electric mixer 2 minutes or until creamy.
- Gradually add sugar, beating 5 to 7 minutes.
- Add eggs, 1 at a time, beating just until yellow disappears.
- Add flour to butter mixture alternately with milk, beginning and ending with flour.
- Mix at low speed just until blended after each addition.
- Stir in vanilla.
- Combine 1 cup batter and chocolate syrup, stirring until blended.
- Divide remaining batter in half; pour 1 portion into a greased and floured 10-inch tube pan.
- Spoon half of chocolate batter on top; repeat layers.
- Gently swirl batter with a knife.
- Bake at 300° for 1 hour and 40 minutes or until a wooden pick inserted in center comes out clean.
- Cool in pan on a wire rack 10 minutes; remove from pan, and cool completely on a wire rack.