Melt the butter in a 5 quart pot set over medium heat. Add the onion and cook until soft, about 5 minutes. Add the corned beef and cook another 5 minutes, or until the edges begin to curl. Stir in the potatoes and cook 2 minutes. Sprinkle in the flour; stir well.
Stir in the stock and sauerkraut; bring to a simmer. Simmer for 15 minutes, or until the potatoes are cooked through. Remove from heat.
Slowly stir in the sour cream and cheese. Top with green onions.
Keyword Beef, Dinners, Easy, Easy Dinners, Lunches, Simmered, Soups, St. Patrick's Day