LINE 13x9-inch pan with foil. Lightly grease foil; set aside.
PLACE sugar, butter, milk and marshmallows in large saucepan; cook on medium heat until mixture comes to boil, stirring constantly. Boil 5 min., stirring constantly. Add peanut butter chips and vanilla; cook until chips are completely melted and mixture is well blended, stirring frequently. Spread immediately into prepared pan. Sprinkle with peanuts; press lightly into fudge.
REFRIGERATE several hours or overnight. Cut into 48 squares. Store in airtight container in refrigerator. For creamier fudge, let fudge stand at room temperature about 1 hour before serving.