Preheat your oven to 400 degrees
Line a standard baking sheet with aluminum foil or parchment paper. Oil a 9 inch spring form pan. Set aside.
To make the sauce:
- Put a 3 quart saucepan over a medium flame and heat the oil. Add the onions and garlic and saute` until the onions are translucent, about 5-7 minutes. Add the tomatoes and salt. Tear the basil by hand into pieces and add it to the pan. Lower the flame to low and simmer for 15-20 minutes stirring occasionally with a wooden spoon. Set aside. And use when ready.
- Bring a large pot of generously salted water to a boil. Drop in the rigatoni and cook about halfway through, about 6 minutes. You want them to be hard so they do not break when filling them.
- Drain the pasta in a colander and rinse with cold running water to stop the cooking process. Drain any excess water and return to the pot. Toss the pasta with 1 cup of the grated cheese making sure to coat all the rigatoni. This will act as a sort of "glue" to hold the pasta together. Set aside.
To make the Filling:
- In a food processor combine the ricotta, spinach, 1 cup of the grated parmigiano, eggs, salt and pepper. Process until very smooth, about 20 seconds.
- Scrape the filling out and into a disposable pastry bag or a gallon sized plastic zipper top bag. Set aside.
- Spread one cup of sauce on the bottom of the pan.
- Snip a tiny corner off the pastry bag or the plastic bag to create an opening no bigger than the rigatoni.
- Start really small and you can always cut the bag some more if you need to. Fill each of the rigatoni with the filling, filling both ends if necessary.
- Stand each of the rigatoni up in the pan and continue until the pan is full. You will use the entire pound of pasta so make sure you squeeze every last one in there!
- Spread the remaining sauce in the jar over the top of the pasta, about 1 1/2 cups and sprinkle with the remains parmigiano cheese.
- Bake for 35 minutes. Add Mozzarella and bake for an additional 10 minutes.
- Let stand for 15-20 minutes.
- Run a knife around the ring to loosen and remove the spring. Cut in wedges and serve!