1. Rinse the couscous in a bowl and drain it in a very fine strainer (line the strainer with cheesecloth if the couscous falls through). Transfer it to a large bowl and rub the grains to be sure they are separate. Set aside to dry for 15 or 20 minutes.
2. Boil 2 or 3 quarts water or bring soup to a simmer in the lower part of couscous pot or steamer. Put the couscous in the couscous pot steamer or in a cheesecloth-lined steamer basket and set it above the boiling water; the boiling water should not touch steamer. If you are using a couscous pot and steam appears to be escaping from the side of the pot, tie a damp towel around the base of the couscous steamer or wrap a piece of plastic wrap around it to prevent the steam from escaping.
3. Steam the couscous, uncovered, for 30 minutes.
4. Transfer the couscous to a large bowl and set it aside just until cool enough to handle. Mix one-half cup water and 1 teaspoon salt until the salt dissolves. Sprinkle the couscous gradually with the salted water, rubbing and tossing it between your fingers to prevent the grains from sticking together.
5. About 30 minutes before serving, return the couscous to the steamer and set it above simmering water. Steam it uncovered until steam comes through the couscous, about 20 minutes. Transfer to a large bowl.
6. Sprinkle the oil over the couscous, tossing lightly with a fork. Slowly add 6 tablespoons broth, tossing lightly. Serve hot, with more broth for moistening the couscous at the table.