Butter six ramekins or custard cups. Melt chocolate and butter slowly: You can do this in a double boiler, over, not in, simmering water, or in microwave, stirring to prevent scorching. Stir until completely smooth.
In a medium bowl, beat eggs with electric mixer until frothy, about 5 to 6 minutes. Stir vanilla and salt gently into beaten eggs. Fold half of egg mixture into chocolate mixture, mix well. Then fold remainder of egg mixture into chocolate mixture. Pour chocolate and egg mixture into prepared ramekins.
Line a roasting pan with a damp kitchen towel. Place ramekins on towel, inside roasting pan. Butter a piece of foil big enough to cover entire pan, and cover the ramekins, buttered side down. Place roasting pan on oven rack. Fill roasting pan with boiling water to reach halfway up the sides of the ramekins. Bake 5 minutes, then remove foil and bake 10 minutes more. Remove ramekins from water carefully. Let cool on wire rack for at least 3 hours. Cakes will firm up as they cool. Unmold each room-temperature ramekin onto a dessert plate, garnish and serve. Refrigerate unused portions.
