Preheat oven to 350°F. Spray a 13×9-inch baking dish with cooking spray.

In a skillet, cook ground beef and onion until browned. Drain fat and set aside.

Layer ¼ of the potato slices in the dish. Season with salt and pepper. Top with ¼ of the beef, then ¼ of the cheese. Repeat this process three more times.

In a bowl, whisk together cheddar soup, evaporated milk, milk, salt, and pepper. Pour evenly over the layers.

Cover tightly with foil. Bake for 1 hour.

Remove foil and bake an additional 15–20 minutes, until potatoes are tender and the top is golden and bubbly.

Let sit for 10 minutes before serving. Enjoy!