For the orange peel, use a peeler to peel the skin off of an orange, peeling it from top to bottom. Remove the pith using a knife.
Cut the peel into a fine chiffonade.
Boil the peel in a small sauce pot with enough water to just cover the peel. Repeat this process two more times, changing the water each time. This will remove any bitter taste.
Cook the peel with the simple syrup in a small sauce pot on medium heat until the peel is translucent. Drain the simple syrup from the peel and cool the peel as soon as possible; it may crystallize if you do not.
Once the candied zest has cooled, transfer it to an airtight container and reserve in the refrigerator. Discard after 5 days.
For candied citron, substitute citron peel for the orange peel.