Preheat oven to 325 degrees. Bring a large saucepan of salted water to a boil. Add the macaroni and cook until slightly al dente, about 8 minutes. Drain and set aside to keep warm.
Whisk the eggs in a large bowl.
Add the Velveeta, 1 stick melted butter and 2 cups of the half-and-half to the large bowl of eggs. Add the warm macaroni tossing until the cheese has melted and the mixture is smooth. Add the remaining half-and-half; 1 cup of the Parmesan cheese, and the remaining shredded cheeses, and salt and pepper, tossing until completely combined in the large bowl.
Pour the mixture into large buttered baking dish.
Melt 4 tablespoons of butter in non-stick fry pan, medium heat. (Now, I use real bread and slice it into cubes about 3/8”, like little tiny croutons.) Add breadcrumbs to the melted butter and fry them for about 2 minutes. Remove from heat. Add 1 cup shredded Parmesan to breadcrumbs. Sprinkle mixture evenly over casserole. Bake covered with foil for 35-40 minutes. Uncover and bake another 15-20 minutes more for a touch of a “crusty” top. Remove, let stand 5 minutes.