How to Make It
Preheat the oven to 325°. In a large skillet, heat 2 tablespoons of the oil. Add the onion, cinnamon and a pinch of salt, cover and cook over moderately low heat, stirring, until the onion is softened, 8 minutes. Add the tomatoes and cook over moderate heat, stirring, until very soft, 8 minutes. Add the wine and boil over high heat for 2 minutes. Add the stock and bring to a boil, then pour into a 9-by-13-inch baking dish.
Season the duck with salt and pepper and set the legs skin side up on the vegetables; keep the skin out of the liquid. Bake the duck legs on the top third of the oven for 1 1/2 hours, until the meat is tender and the skin is crisp.
Meanwhile, spread the hazelnuts in a pie plate and toast until golden, 10 minutes. Transfer to a towel and rub to remove the skins, then transfer to a mini food processor.
In a medium skillet, heat the remaining 2 tablespoons of oil. Add the bread and cook over moderately high heat, stirring, until browned, 2 minutes. Reduce the heat to low and add the garlic. Cook, stirring, until the garlic is golden. Transfer the bread, garlic and oil to the processor and grind coarsely with the hazelnuts.
Transfer the duck to a rimmed baking sheet and keep warm in the oven. Strain the pan sauce through a coarse sieve set over a saucepan, pressing on the solids; scrape the vegetables on the underside of the sieve into the sauce. Skim off the fat. Boil the sauce over high heat until reduced to 2 cups.
Whisk the hazelnut mixture into the sauce and bring to a simmer. Remove from the heat and whisk in the butter. Season with salt and pepper and serve with the duck.