Heat olive oil in a large skillet over medium heat. Brown the ground beef, drain any excess fat, then add chopped onion and minced garlic, cooking until the onion is softened.

Stir in the cream of mushroom soup, milk, salt, and pepper with the beef mixture. Add the sliced potatoes and mix well to coat.

Transfer the mixture to a greased 9x13 inch baking dish. Sprinkle evenly with 1.5 cups of shredded cheddar cheese.

Cover with foil and bake at 375°F (190°C) for 30 minutes. Remove foil, sprinkle with the remaining 0.5 cup cheese, and bake for another 15-20 minutes, or until potatoes are tender and cheese is bubbly and golden.

Let the casserole rest for 5-10 minutes before serving to allow the sauce to set.