Preheat a 4 quart pot over low heat. Spray with cooking spray, then add apples, sweet potatoes, water and salt. Cover pot and sweat the apples and sweet potatoes for about 20 minutes, stirring often. What this means, is just to cook them slowly and let them steam. You want to coax the misture out of them, but if you make the flame too high they’ll burn and cook unevenly.