In a large saucepan, combine 4 cups (1 L) sugar with water 4 cups (1 L) and cinnamon sticks. Cook, stirring, over medium heat until sugar dissolves, about 5 min.
Split the orange slices into 2 batches and place 12 to 15 slices in syrup at a time. Turn heat down and simmer slices 40 to 50 min., turning once, until the pith (the white part of the peel) becomes soft and almost translucent – this is how you'll know the slices have been properly candied. (If the pith remains white, slices may taste bitter.)
Preheat oven to 200°F (100°C). Using heatproof tongs, remove slices from syrup and arrange on a wire rack set over a baking sheet. Dry in the oven for approx. 60 to 75 min., turning halfway through. Remove slices when they are no longer sticky to the touch, but still pliable.
Lightly sprinkle both sides with remaining sugar to absorb moisture. Cool completely.
Melt chocolate in a microwaveable dish on LOW for 60 sec. Check and heat another 30 sec., if required. Dip half of the edge of the peel in chocolate. Let cool and harden on a separate wire rack before packing.
Save leftover orange syrup to drizzle over ice cream and other desserts. Substitute large lemons for the oranges or swap white chocolate for the semi-sweet chocolate.