Cook spinach, drain. Saute onion in butter. Stir in spinach, salt, nutmeg and pepper.
In large bowl combine Ricotta cheese and Parmesan cheese, light cream and eggs; mix. Stir into spinach mixture.
Pour in pastry shell. Bake 425 degrees 15 minutes. Reduce heat to 325 degrees 40 minutes or until custard is set. Insert knife to see if it comes out clean.