1Heat oven to 350°F (325°F for dark or nonstick pans). Make, bake and cool cake as directed on box for two 8-inch or 9-inch rounds.
2Place 1 cake layer, rounded side down, on serving plate. Spread with about 1/3 cup frosting. Top with second layer, rounded side up. Frost side and top of cake with remaining frosting.
3In 1-quart saucepan, heat whipping cream over medium heat until hot (do not boil); remove from heat. Stir in chocolate chips until melted and smooth. Let stand 5 minutes. Carefully pour chocolate mixture onto top center of cake; spread to edge, allowing some to drizzle down side. Garnish top of cake with toffee candy. Refrigerate about 1 hour or until chocolate is set. Store covered in refrigerator.