Sausage Potato Lasagna

Ingredients

• 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