Soak the gelatine in the water with the rind of the lemon for one hour.
Add the sugar and dissolve it over the fire.
Stir and simmer it for a few minutes.
Strain into a basin and add the lemon juice.
When it begins to set, beat in the whites of the eggs, whipped to a very stiff froth.
Whisk until the whole mixture is light and spongy.
Then heap it on a glass dish.
A little of it may be coloured a pale pink with cochineal; and as a decoration, a few pistachio kernels, blanched and chopped, can be sprinkled over the sponge.