Prepare the couscous steamer by wrapping a wet cotton tea towel around the seam where the top and the bottom come together, to prevent steam from escaping. Bring the water in the bottom to a rolling boil, and place the couscous in the top of the couscous steamer. Steam, uncovered, for 30 minutes. Turn the steamed couscous out into a large shallow bowl or on a work surface and, using a wooden spoon, a plastic dough scraper, or your fingers (the couscous is very hot, so be careful) gently break up any clumps in the couscous without mashing it. At this point, if you do not plan to serve the couscous immediately, you may let it sit for several hours. If you plan to serve it soon, spread out the couscous slightly on the work surface, then sprinkle over it an additional 1-1/2 cups (375ml) hot water, 2 to 3 tablespoons at a time. Work it in using a wooden spoon and your fingers by lifting up the couscous and letting it fall through your fingers or from the bowl of the spoon. As soon as the couscous is cool enough for you to handle, work only with your fingers, handling the couscous very lightly until all the water is absorbed. The couscous should be inflated and feel slightly tender, though it will still be quite firm. Let it rest for 10 minutes. Check the cloth tied around the steamer - if it needs moistening, remove and moisten it, then re-tie it around the steamer. Return the couscous to the top of the steamer, bring the water in the steamer to a boil over medium high heat and steam the couscous for 30 minutes. Turn out the couscous into a shallow bowl or a work surface, add the remaining 1 cup (250ml) hot water 2 to 3 tablespoons at a time, working it as before, and let it sit for 10 minutes. Return to the steamer to steam until the couscous is fluffy and tender, about 15 additional minutes.