Slice oranges into ¼-inch rounds with a sharp knife or mandoline.
In a saucepan, combine sugar and water. Heat until sugar dissolves and syrup begins to boil.
Reduce heat to a gentle simmer. Add orange slices in a single layer. Simmer 45–60 minutes, turning occasionally, until peel is translucent.
Remove slices with tongs and arrange on a wire rack. Dry uncovered at room temperature for 24–48 hours until tacky but set.
Optional: Roll in sugar for a frosted finish, or dip in melted chocolate and sprinkle with flaky salt.
