BAKED SHELLS

Steps:

• Bring a large pot of water to a boil over medium heat. Salt the water, add the shells and cook for 2 to 3 minutes less than the package directions. Heads up: Remove and reserve 1 cup of cooking water just before draining.
• Meanwhile, heat a medium-sized pot or high-sided skillet over medium heat with the extra-virgin olive oil. Add the onions and garlic and saute for 3 to 4 minutes. Stir in the spinach, pulling it apart as you add it, and season with a little freshly grated nutmeg and salt, and pepper, to taste. When the spinach mixture is warmed through, transfer it to a small dish and reserve. Return the pot to the heat, add the butter and let it melt. Stir in the tomatoes and break them up with a spoon. Season with salt and pepper, to taste, add the basil leaves, and cook to thicken the sauce, about 7 to 8 minutes.
• Preheat the oven to 400 degrees F.
• Drain the pasta and return it to the hot pot. To the pasta, add the spinach, reserved pasta cooking water, ricotta cheese, and half of the Parmigiano-Reggiano. Adjust the salt and pepper, to taste, and transfer it to a baking dish. Top the pasta mixture with the tomato sauce, mozzarella, and remaining Parmigiano. Bake until the cheeses are melted and bubbly, 6 to 8 minutes. Remove the shells from the oven and serve.