Before you leave home for your camping trip, mix together the flour, sugar, cocoa powder, salt and skimmed milk powder in a small plastic container.
Cut off the tops of your oranges, about an inch from the top to make a flat lid.
Over a bowl, carefully scoop out the flesh of the oranges. This will be a juicy mess, but try and reserve as much of the juice as possible. Wash and dry the oranges.
Mix the orange juice, sunflower and egg with the dry ingredients.
Stir in the coarsely chopped chocolate and spoon the mixture into the prepared oranges, filling each about 2/3 full.
Wrap each orange loosely in aluminium foil, taking care to keep the oranges upright.
Place your wrapped oranges on the edge of your camp-fire, out of direct flame but close enough to the embers to the cakes will bake.
After 25 - 30 minutes remove the cakes from the heat and carefully unwrap. You should see cooked cake peeking out between the orange bowl and lid. Leave to cool for 15 minutes before peeling off the lid.
Eat as it is or with squirty cream kept cool in an ice box.
Use the bottom of another bowl to crush the remaining orange pulp to remove as much juice as possible - there you go, you've got freshly squeezed campfire orange juice!