Preheat oven to 160ºC Coarsely chop 4 Heath bars. Finely chop remaining 4 bars. Reserve separately. CRUST: IN a food processor, grind cookies into fine crumbs. Add melted butter and process until mixed. Press into bottom and about 3 cm up sides of a 24 cm springform pan. Sprinkle coarsely chopped Heat bars over crust. Refrigerate while preparing filling. FILLING: In a 1-cup glass measure, combine half cup cream and coffee crystals. Heat in a microwave oven on HIGH 40-60 seconds, or until coffee dissolves when stirred. Refrigerate until cool, about 15 minutes. IN a large bowl, beat together cream cheese and sugar with an electric mixer on medium speed until smooth, 1-2 minutes. Beat in half cup cream, eggs, and vanilla until well mixed, 1-2 minutes. With mixer on low speed, beat in chilled coffee-cream mixture; continue beating 5 minutes. Turn into prepared crust. Bake 1 hour and 15-20 minutes, or until cheesecake looks set around edges and center still jiggles slightly. Let cake cool; then refrigerate. TOPPING: When cake is cool, in top of a double boiler, heat together chocolate chips and remaining one third cup cream, stirring often, until melted and smooth. Let cool in refrigerator until slightly thickened. Spread topping over cheesecake. Sprinkle finely chopped candy bars on top. Refrigerate until chocolate layer is set and cake is well chilled, 6 hours. Run a knife around edge of pan to loosen cake and remove springform side of pan.