Place the orange slices into a large, wide saucepan then cover with 250 ml (1 cup) of water and bring to a boil.
750 ml water, 2 medium oranges
Simmer for 2 mins then drain slices, discard the water and wipe out the pan.
Add the remaining 500ml (2 cups) water to the same pan along with the granulated sugar and stir gently with a fork to dissolve.
400 g granulated sugar, 750 ml water
Add orange slices and bring to a simmer.
Simmer for 40 - 60 minutes until the pith (the white part between the outer skin and the inner flesh) is translucent - this will depend on the thickness of the slices.
Place a wire rack over a parchment or wax paper-lined baking tray.
Carefully remove slices from the syrup with tongs or a slotted spoon and place on the wire rack in a single layer to cool and set for up to 24 hours.
Sprinkle with caster sugar if using.
caster sugar