Sterilize a glass jar that is big enough to hold the amount of peels you’ll be infusing, by submerging it and its lid in boiling water for 10 minutes. Canning jars are great at handling that kind of heat, so they are a good option, but you can use any kind of jar you have on hand. Pack the peels into the sterilized jar. Cover completely with your spirit of choice. Add the sugar and any spices, if using. Screw the lid on the jar and shake. Place the jar in a cool, dark place for 1 to 2 weeks, shaking every day or so to distribute the flavors. Strain out the peels and spices, compost or discard them, and decant the liquid into another sterilized jar. Enjoy neat or on the rocks. The cordial keeps, in a cool, dark place, for up to 1 year.