With your peeler, remove large strips of peel from your navel oranges, making sure you're avoiding the bitter white peel.
Once you have ¼ cup of fresh peels, place them in your wide-mouth jar together with the vodka and dried orange peels.
Replace the jar lid and shake well.
Store your jar in a cool, dry, dark place to allow infusion of flavors for two weeks, making sure you shake it every day or two days.
Once ready, it's time to make your simple syrup. Place water in your saucepan and bring to a boil over medium heat.
While waiting to boil, place your fine-mesh sieve over a large bowl and cover it with cheesecloth. Slowly pour your orange peel solution into it and allow it to drain.
Wash your infusion jar and allow it to dry.
Once the water in your saucepan is boiling, reduce the heat, then add the sugar and stir using your whisk until completely dissolved.
Allow the solution to simmer for five minutes.
Once done, remove your pan from the heat, and allow the sugar syrup to cool. While waiting, remove the sieve from the bowl and discard the peels.
Once the syrup is cool, measure ¾ cup of it and add it to the orange liqueur in your bowl.
Mix with your whisk until well blended. Taste your liqueur. If it isn't as sweet as you want it to be, add a tablespoon more of the syrup, shake, and taste. Repeat if you need more sweetness.
Transfer the solution to your dried jar, replace the lid, and shake well.
Your homemade Cointreau substitute is now ready to use!