Preheat oven to 350°. Cook macaroni in a 6-qt. stockpot according to package directions for al dente. Drain; return to pot.
In a large saucepan, melt 6 tablespoons butter over medium heat. Stir in flour until smooth; whisk in warmed milk. Bring to a boil, stirring constantly; cook and stir 2-3 minutes or until thickened.
Remove from heat; stir in Gruyere, Cheddar, Monterey Jack cheeses, bacon bits, salt, pepper, and nutmeg. Add to macaroni, tossing to coat.
Transfer to a greased 13x9-in. baking dish. Toss bread crumbs and melted butter, and Italian seasoning; sprinkle over casserole. Then toss the Parmesan cheese on top and Bake uncovered for 30-40 minutes or until bubbly and the top is golden brown.
This recipe is a fast paced job and we suggest a helping hand while cooking this dish.