Brown the beef and onion in a skillet over medium heat for 5-7 minutes, breaking up the meat into small pieces. Drain excess fat and transfer to crockpot.

Wash and thinly slice the potatoes, keeping them in cold water to avoid browning, then layer in the crockpot.

Layer half of the potatoes, half of the beef mixture, and cheese in the crockpot. Repeat with remaining ingredients, ending with cheese on top.

Whisk together the cream of mushroom soup, milk, garlic powder, salt, and pepper, then pour over the layered ingredients in the crockpot.

Cover and cook on low for 6-8 hours until potatoes are tender. Check doneness with a fork.

In the last 15 minutes of cooking, add remaining cheese on top and cover to melt.

Uncover, let it sit for a few minutes, then garnish with parsley or chives before serving.