1 12-ounce package jumbo pasta shells
1 Tbsp olive oil
1 cup finely chopped yellow onion
1 pound sweet Italian sausage, casings removed
1 Tbsp minced garlic
1 large egg
16-ounces ricotta cheese
10-ounces chopped frozen spinach, thawed, squeezed dry, chopped further (or 10 ounces chopped fresh spinach)
1 cup grated Parmesan cheese
1 Tbsp chopped fresh basil or 1 teaspoon dried basil
1/4 cup unseasoned bread crumbs
1/2 teaspoon salt
1/2 teaspoon ground black pepper
1 28-ounce can tomatoes with herbs, including the liquid, tomatoes broken up (or your favorite tomato or pasta sauce)

2 9x13 shallow baking dishes