Preheat oven to 400°F.
In a large stockpot, heat olive oil and brown the sausage, stirring to break up. Once browned, add the tomato-basil sauce and bring to a boil. Reduce heat and simmer 5 minutes*. Spread onto the bottom of a baking dish or casserole. Scatter the spinach over the top of the tomato sauce mixture.
In medium saucepan, melt the butter and combine with the flour. Cook over medium heat, without browning, for about 5 minutes. Add the milk and bring back to a boil, whisking constantly. Once the sauce has thickened, reduce the heat and cook slowly over low heat for 10 minutes, stirring occasionally. Remove from the heat and whisk in half the Mozzarella and half the Parmesan. Season with salt and pepper.
Meanwhile, bring a large pot of salted water to a boil and cook the pasta according to the package directions. Drain and combine with the cheese sauce. Lay this mixture over the top of the spinach in the baking dish. Sprinkle with the remaining cheeses.
Bake until the cheese is bubbly and browned, about 20 minutes.
Approximate Nutritional Information (Per serving):
Calories 920, Fat 47g, Sat. Fat 15g, Trans Fat 1.5g, Cholesterol 170mg, Sodium 3030mg, Total Carbohydrate 31g, Fiber 7g, Sugars 21g, Protein 64g
ALLERGEN INFORMATION: Tree Nut-Free, Peanut-Free, Egg-Free, Soy-Free