Preheat oven to 325 degrees F. Sprinkle the brisket with the coarse salt and pepper. Dredge in flour to coat and shake off any excess. In a large Dutch oven heat oil over high heat. Sear the meat until browned on all sides. Set aside. Reduce heat to moderate and add the carrots and onions. Cook, stirring occasionally, until golden brown, 8 to 10 minutes. Add the garlic and saute 2 minutes longer. Return the meat to the pan along with all remaining ingredients except the salt and garnishes. Bring to a boil, cover the pot and transfer to the oven. Bake for 2 1/2 hours, or until the meat slips off a fork when pierced. Lift out the brisket and place on a cutting board. Cover with a damp towel. Pour the broth with vegetables into a tall container and skim off the layer of fat that rises. Remove and discard the bay leaves and chiles. Pour the broth and vegetables into a blender or a food processor fitted with the metal blade. Puree until smooth, add salt to taste and strain. Reheat the sauce. Slice the brisket against the grain and arrange on a platter. Pour the warm sauce over it, sprinkle with sliced scallions and serve.