Difficulty:[usr 3]
Melt the chocolate over low heat in 3 tablespoons of water. As soon as it is melted, remove from the heat.
Work the butter with a spatula to soften it until the consistency of ointment. Above all, do not heat it to confirm its aroma.
Separate the whites from the yolks. Add the egg yolks one by one to the creamed butter. Then add the icing sugar (sifted if there are lumps) and work the dough well.
Then mix the melted chocolate, flavor with vanilla or coffee. Work the mixture for a long time. Leave to cool completely before incorporating the stiffly beaten egg whites.
Pour into a buttered ribbed pan. Put in the fridge for about 10 hours.
Prepare a vanilla or coffee custard:pour the boiling milk over the yolks and the worked sugar. Thicken over low heat, stirring constantly. Remove from the heat just before boiling, when the cream coats the spoon. Leave to cool.
To unmold, dip the mold for a few seconds in hot water. Invert onto a platter. Surround with custard.
Source:The hundred best desserts at Larousse.