Mix together 125 g (4½ oz) butter and 125 g (4½ oz) caster sugar until soft and smooth. Add 10 egg yolks one at a time mixing well, then cook over a low heat mixing continuously until the mixture coats the back of the spoon. Immediately fold in 7 stiffly beaten egg whites and half fill tall buttered moulds with the mixture so as to allow room for it to rise.
Cook au Bain-marie in the oven for approximately 30 minutes then allow to rest for 10 minutes before demoulding.
Serve accompanied with a fight Sabayon or fruit sauce.