Melt butter in a large heavy saucepan over medium heat. Add oatmeal, and toast, tossing and turning oats, until oatmeal is browned and fragrant, about 4 minutes. Add 4 cups water and salt, and bring to a boil. Reduce to a simmer, cover, and cook until most of the water has evaporated and the oatmeal is tender, about 30 minutes for the Irish oatmeal and 10 minutes for the old-fashioned rolled oats. Serve hot with the toppings of your choice.