The consistency of the batter can be varied by adding more or less liquid. A runny batter will produce a light texture, though it will tend to spread. A thick batter will cling better but will be more stodgy.
Sift the flour and salt into a bowl and make a well in the centre. Stir in the egg yolk, then add the oil and half the water. Beat until smooth, then gradually add the remaining water. Leave to rest for 30 minutes.
Whisk the egg whites until stiff and fold into the batter just before using. The mixture must be used at once in order to obtain maximum benefit from the aeration.
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