Preheat your oven to 375°F (190°C).

In a skillet, cook ground beef and chopped onion over medium heat for 7-10 minutes until beef is brown and onion is translucent. Season with salt, black pepper, and paprika before draining excess fat.

In a medium bowl, mix together cream of mushroom soup, whole milk or heavy cream, and sour cream until smooth.

Grease a 9x13-inch baking dish and layer the cooked beef and onion mixture evenly across the bottom.

Layer the thinly sliced potatoes over the beef mixture, slightly overlapping.

Pour the creamy soup mixture evenly over the potatoes.

Sprinkle shredded cheddar cheese on top.

Cover 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 the casserole rest for 5-10 minutes before serving, then garnish with fresh parsley.