How to Make It
In a very large pot of boiling salted water, cook the pasta shells until al dente; drain well. Rinse under cold water and pat dry thoroughly.
Meanwhile, in a medium skillet, heat the oil. Add the shallots and garlic and cook over moderately high heat until softened and starting to brown, about 1 minute. Add the spinach and cook, stirring, for 1 minute. Transfer to a large bowl and let cool. Add the ricotta and half each of the mozzarella and Parmesan to the spinach. Stir in the parsley and nutmeg and season generously with salt and pepper. Stir in the beaten egg.
Preheat the oven to 375°. Spoon about 1/2 cup of the Spicy Tomato Sauce in each of two 9-by-13-inch baking dishes. Stuff each pasta shell with a heaping tablespoon of the ricotta filling. Arrange the stuffed shells in neat rows in the prepared baking dishes. Spoon 2 cups of the Spicy Tomato Sauce over the shells in each dish. Sprinkle the olives and the remaining mozzarella and Parmesan on top of the pasta and bake for about 50 minutes, until golden and bubbling. Let rest for 15 minutes. Serve the baked shells with the remaining tomato sauce on the side.