Preheat the oven to 375° F.
Cook the pasta shells in a large pot of boiling salted water for nine minutes. Drain and spread them on a clean towel to dry.
Defrost the spinach, drain and squeeze out most of the liquid. In a large bowl, mix the Ricotta with one cup of the Parmigiano
Reggiano, the eggs, the spinach, the chopped basil, and the salt, pepper and nutmeg.
In a 13 x 9 x 2-inch casserole, spread 1½ cups of tomato sauce.
Using a piping bag or plastic bag with one corner cut off, pipe the Ricotta mixture in each shell and place the shells, with opening
up, on the tomato sauce. Fit them snugly against each other.
Cover the shells with the remaining 1½ cups of sauce, then sprinkle with the Mozzarella and the remaining 1/4 cup of Parmigiano
Reggiano. Cover with foil and bake 30 minutes. Remove the foil and bake 10 minutes more. Let stand for at least 10 minutes before