Preheat your oven to 375°F and lightly grease a 9x13-inch baking dish. Peel the potatoes, then slice them into thin, even rounds about ⅛-inch thick. A mandoline slicer makes this easier, but a sharp knife works too.

In a large skillet over medium heat, cook the ground beef and chopped onion for 5 to 7 minutes until the beef is completely browned with no pink remaining and the onions are soft and translucent. Drain excess grease. Season with garlic powder, onion powder, salt, and black pepper. Mix well.

Layer half of the sliced potatoes in the bottom of the greased baking dish. Spoon half of the seasoned ground beef mixture over the potatoes. Repeat with remaining potatoes and beef.

In a small bowl, whisk together the cream of mushroom soup and milk until smooth. Pour this mixture evenly over the casserole layers.

Sprinkle the shredded cheddar cheese over the top and drizzle with melted butter. Cover tightly with aluminum foil and bake for 45 minutes.

Remove the foil and bake for an additional 15 minutes until the cheese is bubbly and golden. Let rest for 5 to 10 minutes before serving. Garnish with paprika if desired.