Prepare pasta according to package directions, until just al dente. Drain; rinse with cool water.
Meanwhile, in large mixing bowl, combine half & half, egg, mustard, salt and white pepper, until well mixed.
Stir in ¾ cup Cheddar cheese, ¾ cup Monterey Jack cheese, ½ cup Parmesan cheese and processed cheese; add macaroni and stir until well combined. Transfer to a greased 2-quart baking dish.
Bake, uncovered, in a preheated 350°F oven 20 minutes. Stir and sprinkle with remaining cheeses. Continue baking until cheese is melted and bubbly (about 15 minutes).
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