Sausage Potato Lasagna

1 lb. bulk italian sausage or bulk pork sausage
2 cups mushrooms, thinly sliced
1 medium onion, chopped
2 cloves garlic, minced
1 tablespoon all-purpose flour
1/2 teaspoon salt
1/4 teaspoon ground white pepper
1/4 teaspoon ground nutmeg
1 cup milk
1-15 ounce carton ricotta cheese
1-10 ounce package frozen chopped spinach, thawed, well drained
1/2 cup parmesan cheese, grated
1 egg, slightly beaten
4 cups refrigerated sliced potatoes
2 cups mozzarella cheese, shredded

In a large skillet, cook the sausage, mushrooms, onion, and garlic over medium heat until sausage is brown. Drain off fat. Stir in flour, salt, white pepper, and nutmeg. Stir in milk. Cook and stir until thickened and bubbly, set aside.

In a medium bowl, stir together ricotta cheese, spinach, parmesan cheese, and egg.

Grease a 3-quart rectangular baking dish. Layer half of the sliced potatoes in the prepared dish. Spread half of the spinach mixture and half of the meat mixture on top. Sprinkle with half of the mozzarella cheese. Repeat with remaining potatoes, spinach mixture, and meat mixture. Set remaining mozzarella cheese aside.

Bake, covered, in a 350 degree F oven for 25 minutes. Uncover and sprinkle with remaining cheese, bake about 10 minutes more or until cheese is melted and mixture is bubbly around edges.

Let stand 10 minutes before serving.