Cook over medium high heat and bring to boil. The cranberries will begin to pop.
Boil, stirring constantly for 10-15 minutes or until the sauce begins to reduce and thicken.
Reduce heat to medium low and allow it to simmer away for another 10-15 minutes, stirring often.
Remove from heat. Allow to cool down, then put it in the refrigerator for at least 2 hours but overnight is best.
Notes
Let it thicken off the heat. Cranberries are loaded with natural pectin, which sets the sauce as it cools. It will look thin in the pot and firm up in the fridge, so do not keep boiling to thicken it.
Stop the bitterness before it starts. Use only the colored outside of the orange peel, not the white pith, and stir the zest in toward the end.
Expect the pop. As the berries heat they split and pop. That is the sauce thickening. Keep a lid handy if your stovetop splatters.
Chill at least 2 hours. Overnight is better. The flavor settles and the texture sets.