Bolognese Sauce: Melt butter with the olive oil in a large saucepan over medium-high heat. Add the chopped onions, celery, and carrots and sauté for two minutes. Add the garlic and sausage to the pan and cook until no longer pink. Sprinkle in the salt, pepper, Italian seasoning, and red pepper. Stir in the milk and allow the mixture to simmer for about 5 minutes.

Add the crushed tomatoes, tomato sauce, tomato paste, and beef broth. Bring to a boil, then lower the heat and simmer for 15 minutes.

Creamy Bechamel Sauce: While the Bolognese sauce simmers, melt 4 tablespoons of butter in a large pan then add and whisk flour. Stir constantly to combine and create a roux for 1-2 minutes. Gradually whisk in the milk. Add the salt, pepper, and garlic powder. Keep whisking the bechamel sauce constantly to ensure that it doesn't burn and continue to cook over medium-low heat. Cook until the sauce begins to thicken and stick to the back of a spoon, about 5-7 minutes.

Layer the Lasagna: Grease the bottom of a 9x13 baking pan and add about ½ cup of Bolognese sauce to cover the bottom. Add a layer of oven-ready uncooked lasagna noodles. Layer ⅓ of the remaining red sauce, ⅓ of the white sauce, ⅓ of the Parmesan, and ⅓ of the mozzarella. Repeat these layers two more times, using up the remaining ⅔ of ingredients.

Grease a piece of aluminum foil and cover the lasagna dish. Bake for 40 - 45 minutes at 375 degrees. Remove the foil and bake for an additional 5 minutes. Let the lasagna sit for 10-15 minutes before cutting and serving.