Wash the apple well.
Use a box grater to shred the apple.
Place the shredded apple into a clean quart-size mason jar.
Crush the cinnamon stick lightly and add it to the jar.
Pour the honey over the apple and cinnamon.
Pour the apple cider vinegar into the jar.
Stir with a clean spoon or butter knife.
Place the lid on the jar and shake until the honey is dissolved.
Set the jar on the counter out of direct sunlight.
Let the shrub sit for 4 days.
Once a day, loosen the lid to burp the jar, then tighten it again.
Shake the jar daily to keep the apple covered and the honey mixed in.
After 4 days, taste the shrub.
Strain out the apple and cinnamon with a fine mesh strainer or cheesecloth.
Transfer the strained shrub syrup to a clean bottle or jar.
Store in the refrigerator.
To serve, mix 1 part shrub syrup with 3 parts sparkling water, club soda, water, tea, or drink of choice.