Cut cake into 1 cm slices and halve each slice diagonally. You will have triangular pieces of cake. Line bottom of 23 cm springform pan with cake, filling in any spaces by cutting some slices into small pieces. Spread half the ice cream over cake. Freeze until firm, about 1 hour. Spread half the fudge topping over ice cream and sprinkle with half the crushed Heath bars. Repeat layering with remaining cake, ice cream, fudge topping and candy. Cover tightly with plastic wrap and freeze until ice cream is set. Before serving, remove pan sides. Place cake on platter. Spread some whipped cream on sides of cake. Pipe rosettes of cream around edge of cake. Serves 8-10.