Quarter potatoes and place in a large pot, add enough salted water to cover
Bring to a boil. Boil gently for 25 minutes or until tender
Let potatoes cool, peel them, and cut into 1/4 inch thick slices
In a medium sized bowl, combine the soup and milk, stirring well
Arrange half the potatoes in the bottom of a greased 2 quart casserole dish; arrange half the sliced onions on top and sprinkle half the cheddar cheese over them
Add salt and pepper to taste
Put half the soup mixture over the potatoes
Repeat layers and put remaining soup mixture over top
