You can start with medium high heat, but you need to stir until the sugar has dissolved.
Let the cranberry mixture come to a boil. The cranberries will begin to pop open. You can see the cracks in the ones at the top. Continue cooking them until they have all popped. You can tell by listening. Now let the mixture cool and then chill it in the refrigerator.
This sauce will keep well, and you can also freeze it. Thus, you can make it several days ahead of when you plan to serve it.
Happy Cooking,
Ruth Ann