Slice off tops and bottoms from 3 large oranes. Cut off the peels with white pith attached. Eat the fruit that is left. :) Slice peels lengthwise into ¼"-wide strips.
Cook peels in a large pot of boiling water 15 minutes; drain, rinse, then drain again. If using lemon or grapefruit, do this twice.
Bring 3 cups of sugar and 3 cups water to a boil in a medium saucepan, stirring to dissolve sugar. Add peels, reduce heat, and simmer until very soft, 40–45 minutes; drain.
Toss peels with remaining sugar on a rimmed baking sheet to coat. Transfer peels to a large sheet of foil and let sit until dry, 1–2 days.
You store your candied peel at room temp for about a month (trust me, it will be eaten long before then) or in the freezer for 2 months.