1. Line 8- or 9-inch square pan with foil, extending foil over edges of pan. Remove wrappers from peanut butter cups.* Cut each cup into quarters; set aside.
2. Combine sugar, evaporated milk and butter in heavy medium saucepan. Cook over medium heat, stirring constantly, to a full rolling boil. Boil, stirring constantly, 5 minutes.
3. Remove from heat; stir in marshmallows, milk chocolate chips and vanilla. Stir until marshmallows are melted. Add peanut butter cup pieces; stir quickly to distribute candy pieces throughout mixture. Spread evenly in prepared pan.
4. Refrigerate 1 hour or until firm. Remove from pan; peel off foil. Cut into squares. Store tightly covered in cool, dry place.
About 2-1/4 pounds fudge.
*Wrappers are easier to remove if candies are placed in freezer for about 15 minutes.