1. Heat oven to 350 degrees. Place raisins in a small bowl, and cover with hot water. Let soak until plump. Drain, and set aside.
2. In a large bowl, whisk together 4 whole eggs, sugar, and salt. Whisk in 2 1/2 cups milk and 1 1/2 teaspoons vanilla extract.
3. Butter a 9-inch, 1 1/2-quart ceramic baking dish with sides that are at least 1 1/2 inches high. Sprinkle bottom of dish with brown sugar; arrange half the challah cubes in a layer on top. Sprinkle with half the reserved raisins. Repeat with remaining challah and raisins.
4. Pour the milk-and-egg mixture over the bread, making sure to soak every piece. Transfer baking dish to the oven, and bake until the custard sets and the bread pudding becomes a rich, golden color, 50 to 60 minutes. If bread becomes too brown before filling is set, loosely cover top of pudding with aluminum foil. Allow to cool slightly before serving.
5. Meanwhile, prepare the rum sauce: Combine remaining 1 1/2 cups milk, the heavy cream, and confectioners' sugar in a saucepan; place over medium heat, and heat just until bubbles form around the edges. Remove from heat.
6. Prepare an ice-water bath, and set aside. In a medium bowl, whisk egg yolks with remaining teaspoon vanilla. Slowly beat 1/4 cup of the hot milk mixture into yolks, then slowly whisk yolk mixture back into saucepan with remaining milk mixture. Cook over low heat, stirring constantly, until mixture is thick enough to coat the back of a spoon, about 1 minute.
7. Strain the mixture into a bowl set in the ice-water bath. Stir in rum and remaining 2 tablespoons butter; stir until combined. Let stand until mixture is chilled. Serve bread pudding warm or at room temperature, with the rum sauce on the side.

Yield: 10 servings