Meanwhile, in small microwavable bowl, microwave chocolate chips and whipping cream uncovered on High 30 to 50 seconds; stir. Continue to microwave in 10-second increments until chips can be stirred smooth. Let stand at room temperature 20 to 25 minutes, stirring occasionally, until slightly thickened and still pourable. Pour chocolate mixture over top of cake to cover, letting some drip down side. Return cake to refrigerator about 30 minutes or until chocolate sets up. If refrigerating cake longer than 30 minutes, let cake stand 15 minutes before cutting. Store loosely covered in refrigerator.