Preheat oven to 180 C / Gas 4. Grease a 20x30cm baking dish.
Bring a large pot of lightly salted water to the boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
In a large bowl combine hot cooked macaroni, Emmental, mozzarella and Cheddar and stir until cheeses melt. Stir in milk and season to taste with salt, onion powder, garlic granules and parsley. Spoon into prepared dish, and dot with margarine.
Bake in preheated oven 50 to 60 minutes, or until top is crunchy.