Preheat oven to 350°. In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Season with salt and pepper.
Transfer to a greased 2-qt. baking dish. Top with potatoes. Combine soup, milk and Hidden Valley® Original Ranch® Seasoning & Salad Dressing Mix Shaker; pour over potatoes. Sprinkle with cheese. Bake, uncovered,until heated through, 30-40 minutes.