Separately heat up your apple cider and a cup of water in your preferred method (kettle or microwave, we don’t judge here) at the same time.
Pour the hot water into a mug or a highball glass. Immediately dump the water out, and while the glass is warm, pour in the simple syrup; swirling it around so that it coats the sides of the glass.
Add your hot apple cider and whiskey. Garnish with a cinnamon stick and/or apple slice, and enjoy!