Spinach-Ricotta Stuffed Shells

I altered this recipe just a little bit so I'll include both the original and my changes. It was good - my whole family liked and ate it.

1 lb fresh spinach (I used a little less, maybe 3/4 lb)
1 Tbsp chopped onion (I used onion powder)
1 Tbsp butter
1 beaten egg
2/3 c ricotta cheese (I used a full cup)
1/2 c. grated Parmesan cheese
1/8 tsp ground nutmeg
1 qt tomato sauce (I used a 16 ounce can, I don't know how much a quart is)

In a large saucepan combine the spinach with a small amount of water. Simmer, covered, for 3-5 minutes. Drain well. Squeeze the spinach to remove the excess moisture. Chop the spinach. In a skillet cook onion in butter until tender, but not brown. Add spinach, heat through. Combine egg, ricotta, Parmesan and nutmeg. Then add the spinach mixture. Pour half the sauce in a baking dish. Stuff 2o (I stuffed 16, that's how many fit in my pan) shells with filling, arrange in dish and top with remaining sauce. Bake at 350 degrees for 30 minutes.
I put most of my sauce in the bottom, since not everyone is a big fan of tomato sauce at my house. I wasn't sure if I should cover the dish. I tried not covering it but it looked like it was getting dried out (maybe because I didn't put the sauce on top?) and so I added the lid halfway through. They turned out really good!