How to Make It
Preheat the oven to 325°. In a heatproof bowl, soak the dried porcini in the 1 cup of boiling water until softened, about 20 minutes. Rub the mushrooms together to loosen any grit, then remove them from the water and coarsely chop. Let the soaking liquid stand for 5 minutes to settle, then pour it into a clean bowl, leaving any grit behind.
Heat the olive oil in a medium enameled cast-iron casserole. Add one-third of the meat at a time, season with salt and brown well on all sides over moderate heat, about 6 minutes; transfer to a plate. Repeat with the remaining meat.
Add the carrots and onions to the casserole and cook, stirring, until lightly browned, about 10 minutes.
Discard any fat in the casserole. Sprinkle the flour over the vegetables and cook until it browns lightly, about 3 minutes. Gradually stir in the wine and the 2 cups of water, scraping up the browned pan juices. Return the meat to the casserole. Add the tomato paste, bay leaves, thyme and the porcini and their soaking liquid. Bring to a boil.
Cover the casserole tightly and bake for 3 hours, or until the cubes of beef are very tender. Discard the bay leaves and the thyme sprig and skim the fat from the sauce. Season with salt and pepper and serve.