Bring the water to a boil, add all the ingredients of the court bouillon, and cook, covered, at a light boil for ½ hour. Strain the liquid, discard the solid elements, and cook the chard ribs in it, covered, at a light boil, for about 12 minutes—or until tender. Transfer them with a large wire skimming spoon to a gratin dish and grind pepper over the surface.
Pound the anchovy filets and the garlic cloves to a paste in a mortar.
Cook the olive oil and the flour together for a minute or two over a tiny flame, stirring, add the anchovy-garlic paste, the parsley, the cayenne, and the saffron, stir well together, and add the court bouillon, the first cupful in small quantities at a time, stirring the while to avoid lumping. Continue stirring until the boil is reached and leave to simmer—or to boil very lightly at one part of the surface, skimming off the skin that forms two or three times over a period of 20 minutes. Taste for salt. Pour the sauce evenly over the ribs and put into a hot oven (450°) for another 20 minutes.