Pour the water over the porcini, stir, and set aside for at least 30 minutes. Retrieve the mushrooms with a slotted spoon onto a double layer of paper towels. Dry lightly, then coarsely chop. Strain porcini liquid, through a fine sieve into a cup or bowl, leaving behind any sediment that may have accumulated.
Place the bread cubes onto two rimmed sheets and bake at 325 or 350 for 10-15 minutes, or until dried lightly. Remove and place in a bowl or cool on sheets.
Put the butter, leeks, shallots, button mushrooms, and shiitake mushrooms into a heavy sauté pan, 12-inch skillet, or oven casserole, and turn the heat to medium-high. Cook, stirring often, for about 10-12 minutes, or until golden and softened. Add the celery, porcini, 1-cup of the cleared soaking liquid, and salt and pepper to taste. Reduce fully. Sauté a few minutes more, over lower heat. Stir in parsley, hazelnuts, and herbs. Transfer to bowl with bread. Stir to combine. Taste for salt and pepper. Stir in the eggs.
To do the stuffing in a turkey, use it just as it is. The remainder will need to be moistened with a mix of chicken stock and reserved mushroom liquid. Moisten lightly, and put into a greased casserole dish of suitable size. Cover with foil and bake for about 30 minutes, alongside the turkey, uncover to bake 10-20 minutes more, to crisp.
To do entirely in a dish, combine stock and liquid, use to moisten stuffing cubes, not allowing it to become to soaked, not all of the liquid will be used. Transfer to a greased 4-quart dish, cover with greased foil and bake slow, at 325 for an hour, uncover and bake 10-15 minutes more.