Preheat oven to 350 degrees. Butter a 9 inch fluted tube pan. In a medium saucepan, combine candy and 1/2 cup of the butter or margarine. Melt over low heat, stirring until smooth. In a large mixer bowl, cream remaining 1/2 cup butter or margarine and sugar. Add eggs one at a time. Beat well after each addition. Add vanilla and melted candy. Beat until light and fluffy. Combine flour and baking soda. Add alternately with buttermilk to batter. Fold in nuts. Pour into prepared pan. Bake 1 hour and 20 minutes or until wooden pick inserted near center comes out dry. The top will be quite dark. Cool in pan 10 minutes. Remove from pan. Cool completely on wire rack. Frost, if desired. Makes 10 to 12 servings.