Place the chicken pieces in a large bowl and add the chopped onion, garlic, wine, salt, and pepper. Cover with plastic wrap and refrigerate for 4 hours or overnight.
Use tongs to remove the chicken from the wine marinade. Carefully drain the wine through a colander into another bowl and reserve. Transfer the wine-soaked onion and garlic in a separate container and set aside. Season the chicken all over with salt and pepper. Set aside.
Heat a large Dutch oven over medium heat and add the bacon. Cook until crisp and then use a slotted spoon to transfer the bacon to a paper towel-lined plate. Leave the rendered grease in the pot.
Still over medium heat, and working in batches, add the chicken into the hot bacon grease. Sear for 4 minutes. Flip the chicken pieces over and sear for another 4 minutes. Remove the chicken and set aside.
Add the wine soaked onion mixture to the pot and cook until soft and translucent, about 8 minutes. Stir in the flour and cook for another 2 minutes.
Meanwhile, in a small saucepan bring 1 cup of water to a boil. Pour the hot water over the dried porcini mushrooms in a heatproof bowl. Let stand for 20 minutes. Drain the porcini mushrooms and reserve 1/4 cup of the porcini soaking water.
Add the chicken and cooked bacon back into the pot. Pour in the chicken broth and reserved wine. Chop the porcini mushrooms and add them along with the reserved 1/4 cup mushroom soaking water and the bouquet garni. Simmer for 30 to 40 minutes, or until chicken is cooked through, but not falling off the bone.
While the chicken is simmering, heat 1 tbsp of butter in a saucepan over medium heat. Add the pearl onions and sauté, stirring occasionally, until lightly browned. Remove from the pan and set aside.
Add 2 more tablespoons butter to the same saucepan and stir until melted. Add the sliced button mushrooms and sauté until soft and just releasing their liquid, about 7 minutes. Remove from the pan and set aside.
Once the chicken is tender and cooked, remove the pieces from the sauce on to a plate and loosely tent with a piece of foil. Stir in the pearl onions and mushrooms, and let the sauce simmer on medium-high until slightly reduced and thickened, about another 10 minutes.
Return the chicken to the pot and serve at once.
This nutritional information refers to each serving of the entire recipe and not just the products used as ingredients.