Combine 1 1/2 cups hot water and dried porcini in small bowl. Let stand until mushrooms soften, about 30 minutes. Using slotted spoon, transfer mushrooms to work surface; chop finely. Pour mushroom soaking liquid into small bowl, leaving any sediment behind, and reserve.
Add chanterelle mushrooms to a large dry skillet and cook over medium-high heat until most of the water evaporates. Add butter and button mushrooms; sauté 10 minutes. Add leeks and garlic; sauté 5 minutes.
Add wine, thyme, and porcini mushrooms. Cook until almost all wine evaporates, stirring occasionally, about 5 minutes. (Can be made 1 day ahead. Cover mushroom mixture and porcini soaking liquid separately and chill. Reheat mushroom mixture to lukewarm before continuing.) Transfer mixture to very large bowl.
Mix bread into mushroom mixture. Season with salt and pepper; mix in egg.
To bake stuffing in dish:
Preheat oven to 350°F. Generously butter 13x9x2-inch glass baking dish. Add enough reserved mushroom soaking liquid to stuffing to moisten (3/4 cup to 1 1/4 cups). Transfer stuffing to prepared dish. Bake uncovered until heated through, about 40 minutes.
To bake stuffing in turkey:
Loosely fill main cavity and neck cavity of turkey with stuffing. Add enough mushroom soaking liquid to remaining stuffing to moisten slightly (1/4 cup to 3/4 cup, depending on amount of remaining stuffing). Generously butter baking dish. Spoon remaining stuffing into prepared dish. Cover dish with buttered foil, buttered side down. Bake stuffing in dish -- alongside turkey or while turkey is resting -- until heated through, about 25 minutes. Uncover stuffing in dish. Bake until top of stuffing is slightly crisp and golden, about 15 minutes longer.
Adapted from Bon Appétit, November 2002, by Rochelle Palermo Torres