To make the red sauce, heat the olive oil in a large skillet over medium heat. Add the onion and garlic and cook until soft, about 5 minutes.

Add the ground beef, sausage, Italian seasoning and cook until meat is no longer pink, breaking up the meat as you go. Add the crushed tomatoes and broth and bring to a simmer. Stir in the sugar, then salt and pepper, to taste. Simmer, partially covered for about an hour.

Meanwhile, prepare the white sauce by melting the butter in a medium saucepan over medium heat. Stir in the flour.

Gradually whisk in the milk and cream, and bring to a simmer. Stir in the nutmeg, Parmesan cheese and salt and pepper, to taste. Cook until cheese is melted and sauce is thickened.

Preheat oven to 350 degrees. Lightly grease a 9x13 inch baking pan. Cover the bottom of the pan with a layer of the meat sauce. Top with 3-4 lasagna noodles, a layer of white sauce, and 1/4 of the mozzarella cheese. Repeat layers twice more.

Add one final layer of noodles to the top of the lasagna, then top with the remaining meat sauce and the remaining cheese. Reserve additional white sauce to spoon over the lasagna.

Bake, covered, for about 30 minutes. Uncover and bake about 20 minutes more, or until the top is browned and bubbly. Let stand 10-15 minutes before slicing and serving, with extra white sauce on the side.