Line square pan, 9x9x2 inches, with aluminum foil, leaving 1 inch of foil overhanging at 2 opposite sides of pan. Grease foil with butter.
Place chocolate chips, marshmallows and milk in 8-cup microwavable measuring cup. Microwave uncovered on High 3 to 5 minutes, stirring every minute, until marshmallows and chips are melted and can be stirred smooth.
Stir in vanilla, nuts and cherries. Immediately pour into pan. Drizzle with melted white baking chips. Refrigerate about 2 hours or until firm.
Remove fudge from pan, using foil edges to lift. Cut into 9 rows by 8 rows, or cut into diamond shapes.