Preheat oven to 350 degrees F (175 degrees C).
Heat a large skillet over medium-high heat. Cook and stir ground beef in the hot skillet until browned and crumbly, 5 to 7 minutes. Drain and discard grease.
Mix condensed soup, milk, onion, salt, and pepper in a medium bowl until combined. Alternately layer the potatoes, soup mixture, and browned ground beef in a 2-quart baking dish.
Bake in the preheated oven until potatoes are tender, about 1 to 1 1/2 hours. Top with Cheddar cheese, and continue baking until cheese is melted.