Bring large pot of salted water to boil. Add pasta and return to boil. Cook for 6-7 minutes or until slightly less done than al dente (pasta will cook more in the oven). Before draining, reserve 1 cup of pasta water and set aside. Drain pasta and rinse with cold water.
Preheat oven to 350°F.
In large bowl, mix ricotta, half the mozzarella, half the Parmesan cheese, Italian seasoning, salt, nutmeg and spinach.
Add pasta to cheese mix and stir well. Add as much reserved pasta water as needed to have a silky smooth sauce. You don't want it runny, but your pasta shouldn't be sticky and dry.
Cover bottom of 9x13 casserole dish with half of pasta sauce.
Place pasta mixed with ricotta on top of sauce. Pour remainder of sauce on top.
Sprinkle top with remainder of mozzarella and Parmesan cheese.
Cover with aluminum foil and bake for 40 minutes. Remove foil and bake for another 5-10 minutes until cheese bubbles and turns brown.
To Freeze: Do not bake. Cool assembled dish completely. Cover with plastic wrap and aluminum foil or lid. Label with cooking instructions.
To Cook from Frozen: Thaw for 24 hours in fridge. Remove all wrapping, cover with foil and cook at 350°F for 50 minutes, uncover and cook another 5 to 10 minutes. Or bake direct from frozen for 1 ¾ - 2 hours or until heated through and cheese is bubbly and turning golden.
