Wash the oranges and, using a sharp knife, slice off the tops leaving enough space to carve out the insides. Carefully hollow out as much of the orange as you can with a spoon, making sure to keep the bottom intact. Keep all the flesh you've dug out.
Carefully carve pumpkin-style faces in the orange skins using a small sharp knife. Get creative – make them happy, sad or scary little monsters.
Place a sieve over a bowl and, using a spoon, squeeze the orange flesh to produce as much juice as possible. You will need 550ml juice.
Place the sugar in a saucepan over a low heat with 500ml of water and stir until the sugar dissolves. Sprinkle the gelatin or vegetarian alternative over the surface of the water and stir until dissolved. Remove from the heat and stir in the orange juice. Pour the mixture into a high-rimmed baking tray. Leave in the fridge to set for at least 5 hours or overnight, along with the carved orange shells.
When you’re ready to serve, take a fork and drag through the jelly in the baking tray until it’s all mushy. Spoon the mixture into the orange shells, pushing down gently with a spoon so it looks as if it is seeping out of the holes. Pile the jelly on top so it looks as if it is bubbling out. Serve.