Wash lemons, dry, and grate rind finely. Whisk the egg yolks, sugar, rind and lemon juice over hot water until thick and creamy, then remove bowl from the hot water and continue whisking until cool. Soften the gelatine in the ¼ pt. water, and heat to dissolve. Half-whip the cream. Whisk the egg whites very stiffly. Add the gelatine, steaming hot, in a thin stream to the egg mixture, and stir in. Fold in the cream and the stiffly-whipped whites. Fold the mixture very lightly until setting is imminent—the mixture pulls against the spoon. Pour into the soufflé dish and leave to set. Remove the paper band by coaxing it away from the mixture with a knife dipped in hot water. Decorate the sides with chopped, blanched pistachio nuts, and the top with piped cream, if liked.