Preheat the oven to 350 degrees Fahrenheit. Grease a 13×9 baking dish with butter.

Cook macaroni according to package directions for al dente, or even slightly less time. (I cooked mine for 7 minutes.) Drain and set aside.

Combine milk and broth and set aside.

Melt the butter over medium heat. Add flour and let cook for 2 minutes, constantly stirring, so the flour doesn’t burn. Add milk and broth mixture in three additions, constantly whisking and making sure the liquid is well mixed before adding more. Continue whisking the mixture over medium heat until bubbly and thickened, about 7 to 10 minutes. Add the beef and let the sauce thicken.

Remove from heat. Add both kinds of cheese and stir until melted and blended. Add nutmeg. Adjust taste with salt and pepper.

Combine cheese mixture with pasta. Spread in prepared pan. Top with tomato slices. Sprinkle bread crumbs over the tomatoes.

Bake the mac and cheese for 20 minutes, or until cheese is bubbling. Broil for an additional 5 minutes to toast breadcrumbs. Remove the mac and cheese from oven and let sit for a few minutes before serving.