Preheat the Oven:

• Preheat your oven to 375°F (190°C).

Cook the Beef:

• In a large skillet, heat olive oil over medium heat. Add the ground beef and cook until browned, breaking it apart with a spoon as it cooks. Drain any excess fat.
• Stir in the chopped onion and cook until softened, about 3-4 minutes.

Prepare the Sauce:

• In a medium bowl, combine cream of mushroom soup and milk. Mix until smooth.
• Stir in garlic powder, paprika, and salt and pepper to taste.

Assemble the Casserole:

• Lightly grease a 9×13-inch baking dish with olive oil.
• Layer half of the sliced potatoes in the bottom of the baking dish.
• Spread the cooked beef and onion mixture evenly over the potatoes.
• Pour the soup mixture over the beef and potatoes.
• Layer the remaining potatoes on top.
• Sprinkle shredded cheddar cheese evenly over the top.
• If using, sprinkle grated Parmesan cheese over the cheddar.

Bake:

• Cover the baking dish with aluminum foil and bake in the preheated oven for 45 minutes.
• Remove the foil and bake for an additional 15-20 minutes, or until the potatoes are tender and the cheese is melted and bubbly.

Serve:

• Allow the casserole to cool for a few minutes before serving. Enjoy!