Melt chocolate. Mix butter with salt, sugar and egg yolks. Then add melted chocolate and mix until the mixture is smooth. Whip the egg whites and slowly add vanilla sugar. Put them on the egg yolks mixture and add flour. Mix very gently and slowly. Bake 80 minutes at 160 degrees. Chilled cake cut on half and spread with apricot jam. Spread the top of the cake with jam and pour with chocolate couverture.