In a medium skillet, brown ground beef with onion and garlic. Season with salt and pepper. Drain off fat and set aside. Peel and slice potatoes, set aside. *Use a mandoline slicer to slice potatoes thinly and quickly if preferred.
In a mixing bowl, combine cream of mushroom soup and milk until smooth. Set aside.
In a 13 x 9-inch baking dish. Layer potatoes, ground beef, soup, and cheese. Repeat layers. Top with remaining cheese. Cover with foil and bake for 1 hour
Remover foil and bake another 30 minutes or until potatoes are fork tender.