Preheat your oven to 375°F (190°C).

In a large skillet over medium heat, add the ground beef and cook for 7-10 minutes until browned. Drain excess fat.

Add the finely chopped onion to the skillet and sauté for 3-4 minutes until translucent. Season with salt, pepper, and garlic powder.

Peel and thinly slice the potatoes to about 1/8-inch thick. Layer half of the potato slices in a greased baking dish, seasoning lightly.

Spread the sautéed beef and onion mixture over the first layer of potato slices.

Top with the remaining potato slices, seasoning them again.

Whisk together the milk and melted butter in a small bowl, then pour evenly over the layers.

Sprinkle shredded cheese over the top of the casserole.

Cover with foil and bake for 45 minutes. Remove foil and bake for an additional 15-20 minutes until cheese is golden.

Let it rest for 10 minutes before serving.