BLACK AND WHITE CRèME BRûLéE

Steps:

• For the custard:
• In a heavy medium saucepan, combine the milk, cream, and sugar. Split the vanilla bean and scrape the seeds into the milk mixture. Add the pod and bring to a boil over medium heat. Remove from the heat and let steep for 30 minutes, or until the mixture cools to room temperature. Discard the vanilla pod or reserve for another use.
• Place a rack in the center of the oven and preheat the oven to 300°F.
• Lightly beat the egg yolks with a fork, then whisk into the milk mixture. Strain the custard through a fine-mesh strainer into a 2- to 3-quart shallow gratin dish.
• Place the gratin dish in a large deep baking pan or a roasting pan. Pour enough very hot water into the pan to come three-quarters of the way up the gratin dish. Bake for 45 minutes. Check the custard by gently shaking the dish; the custard should be set but still move slightly. Test by inserting a knife into the custard; it should come out clean and almost dry. If necessary, cook the custard for 5 to 10 minutes longer, checking often.
• Carefully remove the gratin dish from the water bath. Let cool to room temperature, then cover and refrigerate until cold, at least 4 hours overnight.
• For the mousse:
• Melt the chocolate and butter in the top of a double boiler set over gently simmering water, stirring occasionally until smooth. Remove from the heat and let sit in a warm spot until tepid or barely warm. (If the chocolate is too hot when added to the yolks, the yolks could curdle; if the chocolate is too cool, flakes of chocolate may form in the yolks.)
• The mousse is best made with a whisk or with a hand mixer; a stand mixer may not be able to whisk such a small quantity. In a medium bowl, whisk the egg yolks with 1 tablespoon of the sugar until a slowly dissolving ribbon forms when the whisk is lifted. Fold in the tepid chocolate. In a medium bowl, using a clean dry whisk or beaters, beat the egg whites with the cream of tartar until soft peaks form. Add the remaining 1 tablespoon sugar and continue beating until barely stiff peaks form. Gently fold half of the whites into the chocolate mixture, then fold in the remaining whites.
• Spoon the chocolate mousse over the chilled custard, smoothing the top with a small offset spatula. Wipe the rim of the dish with a damp towel to remove any chocolate. Cover with plastic wrap and refrigerate for at least 6 hours, or, preferably, overnight.
• Thirty minutes before serving, remove the crème brûlée from the refrigerator.
• To caramelize the brûlée:
• Sprinkle the sugar in an even layer over the top of the mousse. If using a torch, work from one end of the dish to the other. Adjust the level of the torch as necessary to regulate the heat, moving the flame over the surface to caramelize the sugar. If using a broiler, place a rack on the highest level and preheat the broiler. Broil until the sugar is melted and caramelized, about 2 minutes. Watch carefully, and move or turn the dish as necessary for even caramelization.