Sift the flours and salt together. Combine the water and milk. Put the flour mixture into a mixing bowl. Make a well in the centre and break in the egg and add half the liquid. Work gradually into the flour using a whisk. Beat lightly until well combined and smooth. Add remaining liquid gradually. Whisk gently until the batter has the consistency of pouring cream.
Cover the batter loosely with a piece of cling film wrap and leave in a cool place for 30 minutes.
Lightly brush a pan with oil and heat until just hot. Wipe off excess oil and pour about 3 tablespoons of batter into the middle of the pan. Tilt the pan from side to side so the batter runs into a thin and even layer across the bottom of the pan.
Cook over medium heat for about 1 1/2 minutes or until pancake browns around the edge and begins to curl away from the pan. Slide a palette knife under the pancake and flip it over. Brown the underside for a further minute.
Turn the pancake out of the pan and continue to make the rest of pancakes. Stack the pancakes between sheets of parchment paper until ready to serve.