In a large deep skillet, saute 1 1/2 pounds quartered shiitake mushrooms in 2 tablespoons butter; remove from the skillet.
Season with salt and pepper and add 4 tablespoons butter, 3 chopped celery stalks, 1 tablespoon chopped sage, 8 sliced shallots, 2 minced garlic cloves and 1 diced peeled butternut squash; cook 5 minutes.
Pour in 1/2 cup apple cider; cook 3 minutes, then add 3 cups chicken broth. Simmer until step 5.
In a large bowl, mix 1/4 cup chopped parsley and the sauteed shiitakes.
Add to the bowl 8 cups toasted sourdough bread cubes and the hot broth mixture.
Gently toss the stuffing, then spread in a buttered 9-by-13-inch baking dish. Dot the top with butter or turkey pan drippings, cover and bake 30 minutes at 350. Uncover and bake until golden, 20 more minutes.