Preheat grill. Grease a 1 1/2 litre microwave safe dish.
Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
Microwave frozen macaroni and cheese according to packet directions.
Stir together pasta, macaroni and cheese, milk and pepper in prepared dish. Mix well. Microwave on high 2 minutes until heated through. Sprinkle with Cheddar and Parmesan and place under grill. Grill until cheese is melted and beginning to brown, 2 to 5 minutes.