Add all ingredients except cornstarch and water to a medium sized saucepan over medium heat. Whisk to combine. Bring mixture to a boil, whisking frequently. If you want to use this for a marinade ONLY, remove the pan from heat, allow mixture to cool to room temperature, then use as desired.
To Make a Grilling Sauce
To thicken the whiskey marinade to use as a grilling sauce:Whisk cornstarch and cold water together in a small bowl, then add to the boiling marinade mixture. Whisk to combine and allow to boil for 2 to 3 minutes, or until thickened.