There's nothing mysterious or challenging about candying citrus, and it certainly adds an elegant touch to desserts. The cooking syrup tastes great drizzled over fruit or soaked into layer cakes.
Combine the sugar with 1-1/2 cups of water in a large, heavy-bottomed skillet and bring to a boil over high heat, stirring to dissolve the sugar.
Arrange the orange slices in the pan in a single layer. Reduce the heat to medium-low and simmer the slices, turning occasionally, until the skin and white pith are translucent, 30 to 40 minutes.
Remove the pan from the heat and let the orange slices cool in the syrup, turning them once or twice. Remove carefully from the pan with a small spatula or tongs and arrange the slices in a single layer on a sheet of parchment or wax paper.