Melt candy bars & 1/2 cup butter in a saucepan over low heat. Cream together 1/2 cup butter & 2 cups sugar until fluffy. Add eggs, one at a time, beat well after each addition. Add flour & soda alternately with buttermilk. Stir until smooth. Add melted candy & mix well. Stir in vanilla & chopped pecans. Pour into a greased & floured tube pan. Bake at 350° for 1 hour & 20 minutes, or until done when tested with a toothpick. Cool 15 minutes in pan & then remove. Frost as desired.