Beat butter at medium speed with an electric mixer for 2 minutes or until creamy.
Gradually add sugar and beat 5 to 7 minutes. Add eggs 1 at a time, beating after each addition just until yellow disappears. Add melted candy bars, stirring until well combined.
Mix flour, baking soda, and salt; add to the butter mixture alternately with the buttermilk beginning and ending with the flour. Mix at low speed after each addition just until blended. Stir in pecans, chocolate syrup, and vanilla.
Pour batter into a greased and floured 10-inch tube pan or 12-cup bundt pan.
Bake at 325°F for 1 hour and 5 minutes or until wooden toothpick inserted in center comes out clean. Cool pan on a wire rack for 10 to 15 minutes; remove from pan and cool completely on wire rack.