Heat oven to 325. Butter 9 inch spring from pan. In large bowl, blend chocolate wafer crumbs, finely chopped nuts, and melted butter or margarine. Press into bottom and up sides of prepared pan.
In large bowl, beat cram cheese and 2/3 cup of sugar til smooth. Add eggs one at a time, beating well after each addition. Add melted chocolate chips. Beat well. Add whipping cream, 2 Tbsp. margarine and 1 tsp. vanilla; beat til smooth. Pour into prepared crust. Bake at 325 for 65 to 80 minutes or til center is set. Center of cheesecake will be soft. to minimize cracking, place shallow pan half full of water on lower oven rack during baking. Cool in pan 5 minutes. Carefully remove sides of pan. Cool Completely
In small bowl, mix sour cream, 1 1/2 tsp. vanilla and 1 tsp. sugar; stir til smooth. Spread over cooled cheesecake. Drizzle with 1/2 oz. melted chocolate in lace pattern. Refrigerate several hours or overnight before serving. Garnish as desired. Serves 16