HEAT oven to 350ºF.
COOK shells as directed on package, omitting salt. Meanwhile, brown beef with onions in large skillet; drain. Remove from heat. Stir in 3/4 cup cooking creme, ricotta, 1/2 cup mozzarella and Parmesan.
DRAIN shells; stuff with meat mixture. Spread 1 cup sauce onto bottom of 13x9-inch baking dish; top with shells and remaining sauce. Cover.
BAKE 25 min. Mix remaining cooking creme and milk; drizzle over shells. Top with remaining mozzarella. Bake, uncovered, 5 min. or until cheese is melted.
