In saucepan, combine soup, milk, and cream cheese; cook and stir over medium heat till smooth.
Combine potatoes and onions; stir in soup mixture.
Pour into 10 x 6 x 1 1/2-inch baking dish; cover with foil.
Bake at 350° for 1 1/4 hours, or till potatoes are tender.
Remove foil; top with shredded cheese.
Return to oven to melt cheese.