Preheat oven to 375 degrees.
Spread 1/4 cup Alfredo sauce on the bottom of a 9x13-inch baking dish. Add a layer of noodles over the sauce. If the noodles don't fit, break them up to create an even layer on the bottom.
Microwave spinach for 5 minutes on high, and drain away the liquid. Mix in ricotta cheese and salt.
Spread half of the spinach mixture on top of noodles, sprinkle with a handful of shredded cheese, then place another layer of noodles over that.
Spread remaining spinach mixture on top, sprinkle a little shredded cheese, and drizzle 4 to 5 Tbs. Alfredo sauce on top.
Add another layer of noodles, and spoon remaining Alfredo sauce over it.
Fill empty sauce jar one-quarter full with water (about 1/2 cup) and pour over the noodles.
Spread around so that sauce is distributed evenly, then sprinkle the remaining shredded cheese on top. Bake for 50 minutes, or until cheese is browned and bubbly on the top around the edges. Allow to cool for 15 minutes, then slice into 12 pieces and enjoy.