Soften the gelatine in the water and dissolve.
Heat the milk and add 2 1/2 tablespoons sugar.
Stir to dissolve.
Beat the egg yolks lightly, add a little hot milk to them, then pour back into the milk on the fire.
Cook, stirring almost continuously, till thickened.
Take off the fire and cool for a while.
Add the gelatine.
Stir well.
Cool further.
Add the juice of the lemons and if you like, some of the rind.
Refrigerate till beginning to set.
Beat the cream with 1 tablespoon of the sugar.
Also, beat the egg-whites stiff with the remaining sugar.
Take out the set mixture from the fridge, beat it up and fold in the cream and whites.
Refrigerate till chilled and well set.
Serve decorated with the grated nuts or chocolate.