In a large saucepan over medium high heat, add all of the ingredients.
Bring to a boil and then slightly reduce heat so that it's still bubbling, but won't boil over. Whisk occasionally.
Reduce the liquids by half. You should end up with about 1 cup or less and you'll notice the color darken considerably as you get closer. It will continue to thicken as it cools.
Store any leftovers in an airtight container in the refrigerator.