Dissolve the sugar in the water and boil for 5 minutes. Leave to cool so the syrup becomes thicker; then pour some over the base and walls of the mold to coat.
Break up the egg yolks and whites in a bowl but without beating them, to prevent the formation of bubbles. Pour in the remaining syrup in a thin stream, stirring all the time. Fill the mold with this mixture, cover with the aluminum foil and steam for 20 minutes. When cold, turn out.
Serve on its own or with a raspberry sauce made by blending fresh raspberries with a splash of lemon juice and sugar.
This dessert is often made in very small, bite-sized molds that only need to be cooked in the double boiler for 2 minutes.