1 large head of garlic, top fourth cut off
3 tablespoons extra-virgin olive oil, plus more for drizzling
1/2 cup dried porcini mushrooms
3/4 cup boiling water
1 1/2 pounds skinless boneless chicken thighs, cut into 2-inch pieces
Salt and freshly ground pepper
1/2 pound assorted mushrooms, such as stemmed shiitake, cremini and oyster, quartered
1 tablespoon unsalted butter, plus 2 tablespoons chilled
2 large shallots, thinly sliced
1/4 cup dry red wine
1/2 cup chicken stock
2 medium tomatoes, cut into 1-inch dice
1 tablespoon chopped tarragon
Crusty bread, for serving