Slice the apples. Keep the skins on them if you have a food mill. This will add color and nutrients to your sauce. If you don't have a food mill, then peel the apples.
Dump your apple slices in your cooking vessel along with the cider and cranberries. If you are using a slow cooker, just let your apples cook until they become mush, it may take a few hours. If you are using a pressure cooker, look on your lid and bring to full pressure and then cook for just 1 minute.
Process through a food mill if you left the skins on. Then add any additional sugar to taste.
Serve warm or refrigerate.