It is possible to make this dish with any part of the chicken; I like the thighs because they are succulent and nestle into a pot nicely. If you have fresh mushrooms and want to make a super-classic version of the dish, add them to the sauce before reducing, just as the recipe is written for the dried mushrooms. Pearl onions are what you’ll usually find in coq au vin, but they require a few extra steps, so for something equally tasty and not nearly as laborious, use any standard onion or a few shallots.