Microcook potatoes as directed above or use leftover cooked potatoes. In a large saucepan, cook onion in butter over medium heat for about 5 minutes or until tender, but not brown. Thoroughly stir in flour and the bouillon granules. Add water. Cook and stir until mixture is slightly thickened and bubbly. Add potatoes, evaporated milk, cheese, parsley, Worcestershire sauce, pepper, and salt. Cook and stir over medium heat until cheese is melted and soup is heated through.