Preheat the oven to 375 degrees F (190 degrees C).
Grease a 9 by 13 inch baking dish with butter or cooking spray.
Wash and peel the russet potatoes.
Slice the potatoes into thin, even rounds.
Place a large skillet over medium-high heat.
Add the olive oil to the skillet.
Add the diced yellow onion and cook for 3 minutes until softened.
Add the ground beef to the skillet, breaking it apart with a wooden spoon.
Cook the ground beef for 6 to 8 minutes until fully browned.
Drain the excess grease from the skillet.
Add the garlic powder, onion powder, paprika, black pepper, and salt to the beef.
Stir the seasonings evenly into the beef mixture.
In a mixing bowl, combine the condensed cream of mushroom soup and whole milk.
Whisk the mixture until completely smooth.
Arrange half of the sliced potatoes across the bottom of the prepared baking dish.
Spread half of the cooked ground beef evenly over the potatoes.
Pour half of the creamy soup mixture over the beef.
Sprinkle 1 cup of shredded cheddar cheese evenly over the mixture.
Arrange the remaining sliced potatoes over the cheese.
Spread the remaining ground beef over the potatoes.
Pour the remaining creamy soup mixture evenly over the casserole.
Cover the baking dish tightly with aluminum foil.
Place the casserole in the preheated oven and bake covered for 45 minutes.
Remove the aluminum foil and sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the top.
Return the uncovered casserole to the oven and bake for another 20 to 25 minutes until the potatoes are tender and the cheese is melted, bubbling, and golden.
Remove the casserole from the oven and allow it to rest for 10 minutes.
Sprinkle the chopped fresh parsley over the top before serving.
Serve warm and enjoy! For leftovers, keep the casserole covered and refrigerated for up to 3 days.