Mix ricotta cheese, 2 cups mozzarella cheese, parmesan cheese, egg, parsley, pepper and garlic powder in a bowl. Refridgerate for about 30 mins.
Meanwhile, cook shells according to package directions. Drain, rinse with cold water, drain well.
Spread some spaghetti sauce in bottom of greased 13X9 pan. Stuff shells with ricotta mixture, put in pan. Cover with more sauce and remaining cheese. Bake 350 degrees for 25 mins. Remover foil and continue baking an additional 10 mins. Let rest 10 mins before dishing out.
**I prepared this a day or two ahead of time and kept refridgerated, then popped it in the oven at 375 and baked it for 45 minutes...it was excellent!! It was a huge hit in my house!! It's a basic recipe that can easily be adapted to anyone's taste...add whatever you like to the filling and/or sauce!! Next time I plan to substitute spinach for the parsley in the filling...sort of like a manicotti