Remove the peel from the fruit with a sharp paring knife by first removing the ends of the fruit, then cutting and removing the peel in large segments — avoiding the pith.
Cut the peel into ¼-inch matchstick slices, then boil in 2 cups of water for 10 minutes. (Some fruit peels require multiple changes of boiling water to remove bitterness. Keep a kettle of boiling water ready to expedite this stage.)
Drain the peels and allow them to dry while bringing 2 cups of water and 2 cups of sugar to 230° (use a candy thermometer) while stirring as the sugar melts.
Reduce the heat and add the peels to the sugar syrup — stirring regularly until the sugar mixture thickens and the peels turn a bit translucent.
Remove the peels from the syrup. (Save the simple syrup for flavoring baked goods or an addition to mixed drinks. It can also be saved and used to start a batch of jam, as citrus peels naturally contain pectin, the compound that makes jam thicken.)
Dry the peels overnight on parchment paper or dredge them through granulated sugar and then allow to dry. Store at room temperature in a jar.
Alternative methods of finishing: Leave the peels in the syrup and refrigerate, or use a double boiler to melt some semi-sweet chocolate. Dip the dried peels halfway in the melted chocolate and allow them to set up on parchment paper. Store at room temperature in a jar.