Line a 8 or 9 inch square pan with foil and spray with cooking spray. In a large microwave bowl combine milk, choc. chips, and candy bars microwave for 1 min. then stir, microwave for additional bursts of 20 sec. stirring after each burst, until mixture is smooth. Stir in vanilla. Spread the fudge into prepared pan. Refrigerate for at least 1 hour. Take fudge out of pan by lifting up the foil and transferring it to a cutting board. Cut into small pieces. Keep in covered container.