In a microwaveable bowl stir first 3 ingredients together until well blended. Drop margarine pieces into sugar mixture. Microwave on High 1-2 minutes, or until margarine is melted. Add Rich's milk stirring until smooth. Microwave on High 1-1 1/2 minutes longer until mixture is thick and creamy. Do not overcook.

Stir in vanilla, nuts or marshmallows. Pour into wax paper lined 8" square pan and refrigerate until firm. Cut into squares and enjoy.