Preheat the oven to 325°F. Get out a large, shallow casserole and six custard cups or ramekins that fit inside it comfortably.
Bring a kettle of water to a boil, then remove from the heat.
Pour the cream into a saucepan. Using the edge of a paring knife, scrape the seeds out of the vanilla bean and add to the cream. Heat the cream until hot to the touch (140° to 150°F); do not boil. Whisk briefly to separate the vanilla seeds. Remove from the heat.
Combine the yolks and sugar in a large bowl. Using an electric mixer, beat on medium speed for 3 minutes, or until thick and lemon-color. Add the cream, 1⁄2 cup at a time, stirring with a wooden spoon after each addition.
Strain the mixture through a sieve into another bowl. Divide the custard among the cups and place them in the casserole, evenly spaced. Cover each cup with a small piece of aluminum foil. Pour enough boiled water into the casserole to come one-quarter to one-third of the way up the sides of the cups.
Bake on the center oven rack for 40 to 50 minutes. When done, the custards will be firm near the edge and wobbly but not soupy at the center. They should not puff up. (If this happens, remove from the oven immediately. You may end up with curdled custard.)
Transfer the cups to a cooling rack, uncover, and cool thoroughly. Return the foil lids and chill for at least 4 to 6 hours before serving.