Simmer Grand Marnier and 1/4 cup water in heavy medium saucepan 5 minutes. Cool mixture completely.
Whisk Grand Marnier-water mixture, cream, eggs, sugar, vanilla and nutmeg in large bowl to blend. Place croissant pieces in 13x9x2-inch glass baking dish; add apricots and toss to combine. Pour custard over croissant-apricot mixture, pressing down gently with rubber spatula so that croissant and apricot pieces are evenly covered. Let stand 20 minutes.
Preheat oven to 350. Cover baking dish with aluminum foil. Place dish in larger roasting pan. Add enough hot water to roasting pan to come 1 inch up sides of baking dish. Bake 1 hour.
Remove aluminum foil and continue baking until bread pudding is golden brown on top and firm to touch, about 30 minutes longer. Carefully remove bread pudding from oven and from water bath; cool slightly. Drizzle bread pudding with Caramel Sauce, if desired, and serve warm.