In large sauce pan place butter, cream and bring to boil, slowly add cheddar, Monterey jack cheese stirring constantly until cheese is entirely melted. Once cheese is melted turn off stove and cover melted cheese with lid.
In large mixing bowl, place cooked macaroni, add melted cheese mixture, salt, pepper, garlic powder, onion, egg yolks and diced ham pieces. Stir macaroni, cheese sauce, and ham until well mixed together.
Place in casserole baking dish, garnish top of entrée with toasted breadcrumbs. Place in a 400-degree pre-heated oven. Bake approximately 35 minutes. Remove from oven let stand for about 10 minutes prior to serving.