Peel off the yellow rind of the lemons very thinly, using a potato peeler.
Put in a small pan with the sugar and water and bring to the boil.
Strain on to the gelatine and stir until it dissolves, heating again if necessary.
Allow to cool and then add the lemon juice and the egg white and whisk until stiff.
Pile into glass dishes and garnish with whipped cream, slightly tinted if desired.