1. Preheat oven to 400° with racks in upper and lower thirds. Spray 3-quart baking dish with cooking spray.
2. Put dried porcinis in a heatproof bowl and pour boiling water over them. Let steep 30 minutes. Pour mushrooms with liquid through a paper towel-lined sieve into a bowl, pressing to extract liquid. Reserve 1 cup mushroom water. Transfer porcinis to a cutting board and chop.
3. Arrange bread in one layer in 2 large, shallow baking pans and toast, switching position of pans halfway through baking, until golden and dry (10-15 minutes). Cool; transfer to large bowl.
4. Toast hazelnuts on a baking pan in oven until fragrant (6-8 minutes). Transfer to a kitchen towel and rub off loose skins. Let cool and coarsely chop.
5. Meanwhile, cook shallots in butter and oil in a 12-inch heavy skillet over medium heat, stirring occasionally, until softened and golden (about 6 minutes). Add porcinis and wild mushrooms, celery, sage, and 1/2 teaspoon salt, and cook, stirring occasionally, until liquid from mushrooms has evaporated (20-30 minutes). Add sherry and deglaze skillet by boiling, stirring, and scraping up any brown bits, until sherry is reduced by half (about 2 minutes). Add vegetable mixture to bread in bowl. Add hazelnuts and parsley and toss.
6. Whisk together chicken broth and reserved mushroom water, eggs, remaining 1/2 teaspoon salt, and pepper; stir into bread mixture. Transfer to baking dish. Bake, loosely covered with a sheet of foil, in lower third of oven (30 minutes). Remove foil and bake until top is browned (about 20 minutes more).
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov.