Place the porcini in a bowl. Pour over the hot water and set aside to rehydrate. Meanwhile, heat the oil in a large enameled cast-iron casserole over medium high heat until shimmering. Season the chicken with salt and pepper. Add the chicken without crowding to the casserole. Cook over moderately high heat, turning occasionally, until browned all over, about 5 minutes. Transfer to a plate.

Reduce the heat slightly. Add the onion and cook, stirring occasionally, until clear and translucent, 3 to 5 minutes. Add the mushrooms and cook, stirring occasionally, until no longer squeaky when stirred, about 5 minutes. Add the garlic and cook until fragrant, 45 to 60 seconds then add the wine and cook until almost dry, about 3 minutes. (Add the garlic after the mushrooms are cooked so it’s less likely to burn.)

Remove the rehydrated porcini with a slotted spoon and decant the liquid as described above. Add the porcini, strained porcini broth, crushed tomatoes, bay leaf, and rosemary. Nestle the chicken in the sauce, cover and simmer over moderately low heat until nearly cooked, about 20 minutes. Remove the bay leave and rosemary. Taste and adjust for seasoning with salt and pepper. Serve immediately.