Marinate the chicken: In a large bowl, combine the chicken pieces with the red wine, thyme, bay leaf, and black peppercorns. Cover and refrigerate for at least 4 hours, or preferably overnight.
Prepare the vegetables: Dice the bacon into small pieces. Peel and chop the onions. Slice the mushrooms.
Sear the bacon and chicken: In a large, heavy-bottomed pot or Dutch oven, cook the bacon over medium heat until crisp. Remove the bacon and set aside. Reserve the bacon fat in the pot. Remove the chicken from the marinade and pat dry with paper towels. Season with salt and pepper. In batches, brown the chicken in the bacon fat over medium-high heat. Remove the chicken and set aside.
Sauté the vegetables: Add the onions to the pot and cook until softened, about 5 minutes. Add the mushrooms and cook until they release their liquid and start to brown, about 8 minutes.
Combine and braise: Return the bacon and chicken to the pot. Pour the marinade over the chicken and vegetables. Add the chicken broth. Bring to a simmer, then reduce the heat to low, cover, and simmer for 1 1/2 to 2 hours, or until the chicken is very tender.
Thicken the sauce (optional): In a small bowl, whisk together the flour and butter to form a beurre manié. Stir the beurre manié into the stew and simmer until the sauce has thickened slightly, about 5 minutes. Alternatively, you can reduce the sauce by simmering uncovered for 10-15 minutes.
Serve: Garnish with fresh parsley. Serve hot with mashed potatoes, egg noodles, or crusty bread.
