Cooking the pasta:
- Bring 5 quarts of salted water to a rolling boil.
- Empty contents of 12-ounce package of pasta into boiling water and stir gently. Return to a boil; reduce heat to a very low boil and cook uncovered for about 10 minutes or until almost done al dente. Avoid overcooking.
Shells are often used as a pasta with a sauce over and are cooked until the desired doneness. For the stuffed shells they pasta is cooked slightly underdone in the water and the cooking completed in the oven after filling with the cheese mixture. Overcooking before filling makes fragile pasta that often breaks or splits when trying to fill.
- Drain well, rinse with cold water. Drain well and arrange in a single layer to cool for filling.
Making the filling:
- Clip off the larger stems from the bunch of spinach. Steam or blanch until the leaves are fully wilted. Drain and cool to a safe handling temperature. Squeeze all the water from the spinach, wrap in a kitchen towel or paper towels and wring out the last bit of water. Coarsely chop the spinach.
- Mix together the cheese, eggs, spinach (if used), salt, pepper and nutmeg.
- Fill the pasta with the cheese mixture. The job can be done with a small spoon and a lot of patience, but a piping bag makes the work a lot easier. Handle carefully so as not to tear the cooked pasta. Do not over fill.
- Cover the bottom of a roasting pan or oven-proof serving dish with some of the spaghetti sauce. Arrange the filled pasta in a single layer in the pan. Pour the remaining sauce over the filed shells; the filling should be just above the level of the sauce. Bake at 350°F. for 30 minutes or until hot.
- Add a bit of color with a drizzle of sauce or sprinkle with chopped fresh parsley and additional Parmesan cheese if desired.
Similar three-cheese mixtures are frequently used to fill other large sized pasta such as manicotti or in layered pasta dishes such as lasagna.