Preheat oven to 350°F. Spray 1 1/2 quart casserole with nonstick cooking spray; set aside.

Cook sausage, stirring to separate, in large skillet over medium high heat until no longer pink; drain fat and discard.

Stir together soup, milk, onion, salt and pepper in medium bowl.

Place half of potatoes in prepared casserole. Top with half of soup mixture, top with half of sausage. Repeat layers, ending with sausage. Dot with butter.

Cover pan with foil. Bake 1 1/4 to 1 1/2 hours or until potatoes are tender. Uncover; sprinkle with cheese. Return to oven; bake until cheese is melted and bubbly.