Preparation : Place wine, onion, carrots, celery, garlic, and peppercorns in a large pot and bring to a boil. Reduce heat and simmer for 5 minutes. Let cool completely and then pour over the chicken in a bowl. Drizzle with olive oil, cover the bowl, and let chicken marinate overnight. The next day, preheat oven to 325° F. Remove chicken from marinade and pat dry. Strain marinade, reserving liquid and solids separately. Heat 1 Tbsp. oil over medium heat in a wide, deep pot, such as a Dutch oven. Add bacon and cook until crisp. Using a slotted spoon, transfer bacon to a bowl and increase heat under the pot to medium-high. Brown the chicken in 2 to 3 batches, about 6–8 minutes per batch. Remove chicken from the pot as it is browned and transfer to a plate. Add reserved solids from the marinade to the pot and cook until soft, 10–12 minutes. Sprinkle flour into the pot and cook, stirring, for 1 minute. Whisk in the reserved liquid from the marinade and bring to a boil. Simmer for 2 minutes and then stir in the garlic, stock, and salt and pepper to taste. Place chicken, parsley sprigs, bay leaf, and thyme into the pot with the vegetables. Cover the pot and place in the oven. Bake the chicken until tender, about 1-1 1/2 hours. While the chicken is cooking, heat 1 Tbsp. butter and remaining oil in a heavy bottomed pan over medium heat. Add pearl onions to the pan and cook until golden brown, about 4–5 minutes. Reduce heat to medium-low and cook, covered, until tender, 8–10 minutes. Combine onions with bacon. Heat remaining butter over medium-high heat and cook mushrooms, in batches, until tender. When chicken is cooked, transfer it to a plate and cover with foil to keep warm. Strain the sauce. Serve the chicken on individual plates and top it with the sauce, bacon, onions, mushrooms, and chopped parsley.
