How to Make It
Preheat the oven to 425°. Arrange the chicken pieces, skin side up, on a rack set on a large rimmed baking sheet; season generously with salt and pepper. Roast the chicken in the center of the oven for about 45 minutes, until cooked through and the skin is crisp.
Meanwhile, in a large, deep skillet, heat the olive oil. Add the onion and cook over moderate heat, stirring, until just softened, about 3 minutes. Add the mushrooms, raise the heat to high and cook, stirring occasionally, until softened and lightly browned, about 5 minutes. Add the garlic, bay leaves and thyme and cook until fragrant, about 1 minute. Add the wine and cook until evaporated, scraping up any browned bits, about 5 minutes. Add the chicken stock and simmer until reduced by half, about 15 minutes. Remove the skillet from the heat and stir in the sour cream and yogurt. Discard the bay leaves.
Add the chicken to the sauce, skin side up, and simmer until heated through. Stir in the celery leaves. Transfer the chicken to plates, spoon the sauce on top and serve.