Bring the water and milk to a simmer in a large saucepan over medium heat.
3 cups water, 1 cup lowfat milk
Meanwhile, melt the butter in a skillet over medium heat, then add the oats and toast, stirring constantly, until golden and fragrant, 1 ½ to 2 minutes.
1 tablespoon unsalted butter, 1 cup steel cut oats
Stir the oats into the simmering liquid, reduce the heat,to medium-low, and simmer gently until the mixture is very thick, about 20 minutes.
Stir in the salt and the optional add-ins and continue to simmer, stirring occasionally, until almost all of the liquid has been absorbed and the oatmeal is creamy, about 10 minutes. If doubling the recipe, increase this to 15 minutes. Let stand for 5 minutes before serving.
¼ teaspoon salt, ½ large peeled and grated sweet apple, ⅓ cup dried cranberries, 3 tablespoons brown sugar, ¼ teaspoon ground cinnamon