Place oven rack in top third of oven. Preheat to 200ºC . Cook 20 jumbo shells in large pot in lightly salted water. Stir occasionally until tender, but firm, 10-12 minutes. Drain. Stir together ricotta cheese, egg yolk, quarter cup Parmesan cheese, one third cup finely chopped ham, parsley, oregano, salt and pepper in medium bowl. Spoon 1.5 T. in each shell. Do Not Overfill. Spread quarter cup of spaghetti sauce in 12x9x2 inch glass baking dish or casserole. Arrange shells in single layer. Top with rest of sauce. Sprinkle with quarter cup more Parmesan cheese. Bake at 200ºC . for 15 minutes until hot and bubbly.