Line 8" square pan with foil, with ends of foil extending over sides. Melt 4 chocolate squares in microwave as directed on package; spread onto bottom of prepared pan. Refrigerate 10 minutes or until firm.
Microwave remaining chocolate & milk in same bowl on HIGH 2 - 3 minutes or until chocolate is almost melted; stir until completely melted. Add cream & vanilla; mix well. Spread over chocolate layer in pan.
Refrigerate 2 hours or until firm. Use foil handles to lift fudge from pan before cutting into squares.