Wash the oranges thoroughly and cut off the top and bottom. Make 4–6 lengthwise cuts and carefully remove wide strips of peel. Trim excess white pith if it’s too thick, then cut the peels into ¼-inch strips.
Place the peel strips in a saucepan with cold water. Bring to a boil, then reduce to a simmer for 10 minutes. Drain, rinse, and repeat with fresh water for another 10 minutes to remove bitterness.
In the same pan, combine sugar and water to make a syrup. Heat until the sugar dissolves, then add the blanched peels. Simmer gently for 40–45 minutes until the peels turn glossy and translucent.
Remove peels with a slotted spoon and place them on a wire rack over a baking sheet. Let them sit for 30 minutes. Toss the peels in granulated sugar, shake off excess, and let them dry completely for 24 hours at room temperature.