Preheat oven to 350 degrees.
Lightly grease an 11 x 7-inch baking pan.
Brown ground beef and onion. Drain and set aside.
Mix the mushroom soup, garlic powder, pepper, beef stock and cream in a bowl.
Peel and slice potatoes into 1/8" slices.
Layer half of the potatoes in the bottom of the prepared baking dish.
Pour half the soup mixture over the potatoes.
Top with half the ground beef mixture.
Spread half of the cheese on top.
Repeat with second layer.
Cover with foil and place in pre-heated oven.
Cook casserole for 1 - 1 1/2 hours until potatoes are done.
Remove from the oven and let stand for 10 minutes.