To prepare the custard sauce, heat the milk, sugar and vanilla bean in a 2.5-qt. sauce pan over medium heat, stirring constantly to dissolve the sugar.
In a small bowl, gently whisk the egg yolks. Whisk a little of the hot milk into the egg yolks to warm them.
Add the eggs to the pan and cook the custard, stirring constantly, until it coats the back of a spoon and reaches approximately 170°F/77°C. Test it by drawing your finger across the back of the spoon; if your finger leaves a trail on the spoon, the custard sauce is properly cooked.
To prepare the cakes, preheat the oven to 400°F/205°C. Butter and flour 6 ramekins, (5 - 6 oz. each).
In the top of a 2.5-qt. double boiler, melt the chocolate, butter and Cognac or brandy over medium heat and stir until smooth. Set aside.
In a bowl, beat the sugar and egg yolks until ribboned and lightly colored.
In another bowl, beat the egg whites until stiff. Gently fold the egg whites into the egg yolk mixture.
Sift the flour over the top and fold the flour and chocolate into the egg mixture.
Spoon the mixture into the prepared ramekins, distributing evenly.
Place the ramekins on a jelly roll pan or baking sheet and bake until the cakes have risen and the tops just begin to crack, about 10 - 12 minutes.
Remove the ramekins from the oven and run a knife around their edges. Gently invert the ramekins onto 6 dessert plates.
Spoon the sauce around the edges and dust the tops with confectioners' sugar. Garnish with raspberries or currants and serve warm.