Italian Unstuffed Shells

Name: Italian Unstuffed Shells
Ingredients: Kosher salt and freshly ground black pepper; One 12-ounce box medium pasta shells; One 28-ounce can peeled San Marzano tomatoes; 2 tablespoons olive oil; 1 pound bulk Italian sausage (spicy or sweet); One 20-ounce package frozen chopped spinach, thawed and squeezed dry; 1 cup full-fat ricotta cheese; 1 cup grated Parmesan; 1 cup shredded mozzarella; 1 large egg; 1 clove garlic, minced; Dash nutmeg; 8 ounces sliced fresh mozzarella; 4 to 5 fresh basil leaves, torn