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.