1. Heat a large pot or pan to medium heat with olive oil and add the garlic. Sauté until golden, about 2 minutes, then add the crushed red pepper flakes and cook for another 30 seconds.

2. Add the tomato paste and cook for 5 minutes, stirring frequently. Add a little water if the paste starts to burn. Add the remaining water and the plum tomatoes, bringing the sauce to a lively simmer.

3. Season the sauce with salt and pepper to taste. Turn the heat to low, cover the pot with the lid cracked, and stir occasionally. Mix in the basil a few minutes before assembling the shells.

4. Preheat your oven to 400F.

5. Bring a large pot of salted water to a boil. Blanch the baby spinach for 30 seconds. Drain the spinach, squeeze out excess water, chop it, and set aside.

6. Boil the shells in the salted water until very firm to the bite, about 3 minutes less than package directions. Stir frequently to prevent sticking. Strain the shells, drain them on kitchen towels, and then transfer to a parchment-lined baking sheet to cool before stuffing.

7. Combine the ricotta, 2 cups of shredded mozzarella, 1/2 cup of grated Pecorino Romano, parsley, chopped spinach, and garlic powder. Season with salt if desired. Stir in the 2 beaten eggs until well combined.

8. Ladle a thick layer of sauce onto the bottom of one or two large baking dishes.

9. Fill each shell with the ricotta mixture using a spoon or pastry bag. Arrange the filled shells seam-side up in the baking dish.

10. Top the shells with more sauce, but don’t cover them completely. Sprinkle with the remaining mozzarella and Pecorino cheese. Cover with parchment paper and then aluminum foil. Bake for 20 minutes. Remove the covering and bake for another 15 minutes, until bubbly and crisp. You can broil the top for the last 1-2 minutes, watching carefully.

11. Let the shells rest for at least 10 minutes before serving. Serve with extra sauce on the side.