Place the flour, salt and sugar in a mixing bowl. Make a well in the middle and crack the eggs into it. Using a wooden spoon, begin to mix, incorporating the flour from the edge of the bowl.
As the mixture thickens, gradually add the milk. Mix well after each addition of milk and continue until all the milk is incorporated and you have a smooth batter. Rest the batter for 30 minutes.
For the orange sauce, squeeze the juice from three oranges and pass through a sieve into a pan. Add the finely grated zest of 1 orange and the icing sugar.
Bring the mixture to a boil and reduce by half. Remove from the heat and add the butter. Set aside.
Using a sharp knife, carefully slice off the top and bottom of the remaining orange. Using even, downward strokes, slice the skin away from the flesh and discard. Remove any remaining white pith. Cut between the membranes to segment the orange.
Pour a little oil onto a wad of kitchen paper and lightly wipe the base of the pan to grease it. Pour a little batter into the middle of the pan, tip the pan from side to side and swirl the batter round until the base of the pan is covered. Cook for around 45 seconds then loosen the edge with a pallet knife and flip the pancake over. Cook the other side. The pancake should be golden brown.
Slide out of the pan onto greaseproof paper and repeat to make six crepes. Stack the crepes between greaseproof paper.
Pour the orange sauce into the crepe pan over a low heat. Lower a crepe into the pan and baste with the orange syrup. Using a fork, fold it in half and then half again. Push the crepe to the side of the pan, add a second pancake and repeat with the basting and folding, then repeat with the remaining pancakes. Add a little more water if the pan becomes dry.
Arrange the crepes so they are spread out evenly across the pan, then scatter over the orange segments. Gently heat the Grand Marnier and brandy in a small pan, then pour into a ladle. Set alight and pour over the crepes. Wait for the flames to recede, then serve.