Place oven rack in top third of oven. Preheat to 400 F. 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, 1/4 cup Parmesan cheese, 1/3 cup finely chopped ham, parsley, oregano, salt and pepper in medium bowl. Spoon 1 1/2 T. in each shell. Do Not Overfill. Spread 1/4 cup of spaghetti sauce in 12x9x2" glass baking dish or casserole. Arrange shells in single layer. Top with rest of sauce. Sprinkle with 1/4 cup more Parmesan cheese. Bake at 400 f. for 15 minutes until hot and bubbly.