Challah is an egg-enriched bread that can be found in most bakeries and supermarkets. If you cannot find challah, a firm high-quality sandwich bread such as Arnold Country Classics White or Pepperidge Farm Farmhouse Hearty White may be substituted. If desired, serve this pudding with softly whipped cream or with Bourbon-Brown Sugar Sauce (see related recipe). Store leftovers tightly wrapped in the refrigerator. To retain a crisp top crust when reheating leftovers, cut the bread pudding into squares and heat, uncovered, in a 450-degree oven until warmed through, 6 to 8 minutes.