This is my special recipe for manicotti that I got from my daughters grandma, who is straight from Italy. She said to always incorporate a small amount of cream cheese because it holds things together better than eggs.
Cook pasta as directed, drain, set on a paper towel to dry. Heat a lg skillet over medium heat. Add onion and garlic. Saute until softened.
In a lg bowl, combine ricotta, cream cheese, 1/2 the mozzarella, 1/2 the parmesan, Italian herbs, salt and pepper. Mix until well incorporated. Add spinach and onion/garlic mix. Mix well.
Heat oven to 350. Pour 1/2 the marinara sauce into bottom of a 9" x 13" baking dish. Spoon cheese mix into manicotti shells, ( or pipe it into the shells using a pastry bag.) Arrange shells in pan. Top shells w/ remaining sauce. Cover, bake 30 mins. remove cover and sprinkle w/ remaining cheeses. Cook additional 10 mins or until cheese is melted.