Prepare the Tomato Sauce: In a medium saucepan, warm the olive oil over medium heat. Add the finely chopped shallots (or onion), minced garlic, bay leaf, thyme, and oregano. Sauté gently for about 3 to 4 minutes until the shallots become translucent and fragrant. Stir in the tomato paste and cook for an additional minute to deepen the flavor.
Deglaze with Wine: Pour in the white wine and increase the heat to medium-high. Let the wine simmer briskly until it mostly evaporates, which should take around 2 minutes. This step intensifies the sauce's complexity by reducing the alcohol and concentrating flavors.
Simmer the Sauce: Add the tomato passata, vegetable broth, salt, sugar, and black pepper to the pot. Stir everything together, then reduce the heat to low and let the sauce simmer uncovered for about 20 minutes. This allows the sauce to thicken and develop rich, balanced flavors.
Prepare the Filling: Squeeze out any excess moisture from the thawed spinach using your hands or a clean kitchen towel to avoid watery filling. In a large mixing bowl, combine the drained spinach with ricotta, Parmesan, shredded cheese, egg, minced garlic, nutmeg (if using), salt, and pepper. Mix thoroughly until well blended and creamy.
Assemble the Shells: Preheat your oven to 200°C (400°F) or 180°C (350°F) for fan-forced ovens. Pour the hot tomato sauce into a 9 x 13-inch (23 x 33 cm) baking dish, spreading it evenly. Carefully stuff each uncooked jumbo shell with the ricotta-spinach mixture, packing them generously. Arrange the filled shells in the sauce, ensuring most are covered by the sauce while some may slightly peek above.
Bake Covered: Cover the baking dish tightly with foil or an oven-safe lid to keep moisture in. Place in the oven and bake for 70 minutes. This slow baking allows the shells to cook through gently while soaking up the tomato sauce’s flavor.
Add the Cheese Topping: Remove the foil and sprinkle the shells evenly with shredded mozzarella and Parmesan cheese. Return the dish to the oven and bake uncovered for an additional 15 minutes, or until the cheese is melted, bubbly, and golden.
Serve: Garnish with freshly grated Parmesan and torn basil leaves if desired. Serve warm for a comforting, cheesy, and satisfying meal.