Heat oven to 350

In a large skillet over moderate heat, melt butter and cook onion until lightly browned; cool slightly. In a large bowl beat together 1/3 cup of cream of mushroom soup and add the egg. Stir in bread crumbs and salt. Let crumbs soften about 5 minutes. Add cooked onion and the beef; mix well. Shape into six 1/2 inch thick patties. Arrange in a lightly greased shallow, rectangular 3-quart baking dish.

Bake 30 minutes.

Drain off excess fat. Blend together remaining undiluted soup with the water and pour over the patties. Return to the oven and bake 10 minutes longer.

Source: BigOven