Step 1In a small saucepan, Combine the milk, vanilla bean and seeds in a saucepan. Bring just to a boil. Remove from the heat; infuse for 5 minutes, then strain.
Step 2In an electric mixer or with a whisk, beat the egg yolks with the sugar until pale and thickened. Pour about one-fourth of the hot milk into the egg yolk mixture and mix until well combined, then return the yolk mixture to the pan with the rest of the milk and stir constantly over medium low heat until thickened. Do not allow to boil. Strain into a clean pan and add the liqueur. Chill.
Step 1Heat the oven to 350 degrees. Place the croissant halves on a baking sheet and toast until golden brown, about 8 to 10 minutes. Remove from the oven and cool. Break into half-inch pieces and set aside.
Step 2Heat the cream with the vanilla bean in a saucepan over medium low heat until it just simmers. Remove from the heat; infuse for 5 minutes. Remove vanilla bean.
Step 3In a medium mixing bowl, whisk the egg yolks and sugar together until pale and thickened. Gradually whisk the warm cream into the egg yolks, then return to a clean saucepan. Over medium low heat, bring the mixture to just below a boil, stirring constantly until thickened, about 8 minutes. Immediately remove from heat.
Step 4Combine the croissant pieces and chopped chocolate in a bowl. Divide mixture evenly among 6 (8-ounce) ramekins. Spoon the warm custard over the mixture, pressing down with a fork to be sure all the pieces of croissant are soaked.
Step 5Place the ramekins in a roasting pan and pour in enough very hot water to come halfway up their sides. Bake at 350 degrees, until just set, 25 to 30 minutes. At this stage, the puddings can be cooled and refrigerated for several hours or overnight.
Step 6Before serving, place in a 400-degree oven and heat for 4 to 5 minutes, or until warm throughout. Dust the top of each warm pudding with a little powdered sugar and serve with chilled sauce.