Wash hands with soap and water.

Peel onion and dice into 1/4-inch pieces.

Cook ground beef and onions in a skillet until the meat is browned. Drain off fat.

Add mushroom soup and 1/2 can water. Mix well.

Use a brush to scrub potatoes under cold running water. Slice potatoes into 1/2-inch thick pieces and place in the bottom of a casserole dish.

Spread the meat and soup mixture over potatoes.