Preheat the oven to 250 degrees F.
Butter a large (11 x 8 1/2 x 3 inches) casserole dish and set aside. (Once in the oven, the casserole will sit inside a larger pan. A roasting pan would be good.) Mix the eggs, cream, and vanilla in a large bowl, and combine the sugar, cinnamon, and nutmeg in a separate bowl. This helps to evenly distribute the spices. Add the sugar mixture to the egg mixture, and combine thoroughly.
Place the raisins in the bottom of the buttered casserole, and add the bread slices in a single layer. Gently pour the custard over the bread, making certain that all the bread thoroughly soaks up the custard. Cover the casserole with foil, place in a larger dish (the roasting pan, if that's what you've decided to use) partly filled with hot water, and bake for 2 1/2 hours. Remove the foil, add increase the oven temperature to 300 degrees. Bake for 1 hour more, or until the pudding is golden brown and slightly firm. Use a spoon to make sure the custard is fully cooked; it should be moist but no longer runny. If you're unsure whether it's done, remove it from the oven and let it cool while it remains sitting in the water bath; the carryover effect will keep it cooking but it will not overcook. Serve slightly warm with whiskey sauce.
Bring the cream to a boil, combine the cornstarch and water, and add the mixture to the boiling cream, stirring constantly. Return to a boil, then reduce the heat and cook, stirring, for about 30 seconds, being careful not to burn the mixture. Add the sugar and bourbon, and stir. Let cool to room temperature.
Note: New Orleans French bread is very light and tender. Outside New Orleans, use only a light bread. If the bread is too dense, the recipe won't work.
Recipe Courtesy of Commander's Kitchen (Broadway, 2000) by Ti Adelaide Martin and Jamie Shannon