Preheat oven to 350 degrees. Peel and cut up potatoes and boil. While potatoes are boiling, dice onion and fry in a large skillet until yellow, add ground beef and brown thoroughly. Season with salt and pepper or seasoned salt while cooking.
Drain the fat from the beef and onion mixture. Add the tomato soup and mix in. Then add the green beans. Mix thoroughly. Pour this mixture evenly into a two quart casserole dish.
When the potatoes are cooked, drain, add milk and butter and mash. Spoon on top of the beef mixture and spread around evenly to the sides of the dish covering the beef.