1. Melt the butter in a pan large enough to fit all the chicken pieces in one layer with space for the onion and mushrooms. Once foaming, add the chicken pieces and season them in the pan. Cook the chicken gently until lightly browned on both sides.
2. Add the sliced onion and garlic and evenly spoon over the flour. Add the sliced mushrooms.
3. Increase the heat for a moment, and then deglaze the pan with the wine. Turn the chicken in the wine and flour, and the pour over the crème fraiche to cover the meat.
4. Cover and cook on low heat for 45 minutes. Season to taste.
5. Once cooked (test a thigh with a probe close to the bone, and look for 165˚F), lift out the chicken pieces and serve on a plate with sauce, onions, and mushrooms.