Start by making the sauce, in a large skillet add the olive oil, garlic, onion, carrot and celery, cook on medium heat for 2-3 minutes, then add the tomato puree, water, salt, basil and oregano stir to combine, continue to cook on medium heat, half covered until thickened, approximately 20-25 minutes.
Cook the pasta shells in a large pot of salted water until very al dente. Check the box and boil 2 minutes less then the recommended cooking time. Drain well and set aside, so they don't stick together, toss with a teaspoon or 2 of olive oil.
While the sauce is cooking, in one inch of lightly salted water, cook the spinach until very tender, then drain. Let it cool, once it has cooled, squeeze out as much excess moisture as possible.
Finely chop the spinach. Place it in a medium bowl, add the ricotta, egg, pinch of salt, nutmeg and the parmesan cheese, gently mix together.
In a medium size baking pan spread approximately ¼-½ cup of sauce on the bottom, fill the shells with the ricotta mixture (I used about a heaping teaspoon and a bit per shell). Place the shells in the pan,( the mixture fills 24 shells and they fit perfectly in the pan, I used a an 11x7 inch (28x18 cm)baking dish).
Spoon the remaining sauce over the shells, but don’t cover completely, sprinkle with the 2 tablespoons of parmesan cheese or even some grated mozzarella cheese if you wish, bake in the pre-heated oven for approximately 20-25 minutes. Before serving top with more freshly grated parmesan cheese if desired, serve immediately. Enjoy!
Notes
If you can’t find jumbo pasta shells then you can substitute with cannelloni shells, prepare the same way.If you want you can add some ground turkey, chopped Italian sausage or even ground beef to the sauce, I would advise adding it after cooking the carrots and celery.Any leftovers should be stored in an airtight container and refrigerated. They last about 3-5 days in the fridge.Stuffed shells can be frozen. After stuffing the pasta shells, place on a baking sheet and place in the freezer until they begin to harden.Then, remove from the baking sheet and place in either a freezer bag or an airtight container. When ready to serve, thaw the shells, and continue with the recipe. They will last for up to three months in the freezer.