Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish with cooking spray or a little olive oil.

Heat oil in a large skillet over medium. Add ground beef and break it apart with a spoon. Cook 5–7 minutes until browned. Drain excess fat if needed.

Add chopped onion and minced garlic to the skillet. Cook 3–4 minutes until the onion is soft and translucent. Season beef with a pinch of salt and pepper.

Spread the cooked beef mixture evenly across the bottom of the prepared baking dish. Smooth it into a flat layer.

Arrange thin potato slices over the beef in an even layer. Season the potatoes with salt, pepper, Italian seasoning, and paprika as you lay them down.

Sprinkle the shredded cheddar and grated Parmesan evenly over the top. Pour beef broth (or water) around the edges of the dish so it seeps under the potatoes. If using, drizzle the milk lightly over the cheese for extra creaminess.

Cover the casserole tightly with aluminum foil and bake for 30 minutes. This traps steam so the potatoes cook through.

Remove the foil and bake another 15–20 minutes, until potatoes are tender when pierced with a fork and the cheese is bubbly and golden. If you like a crispier top, broil 1–2 minutes — watch carefully.

Let rest 5 minutes, garnish with chopped parsley if desired, and serve hot.