Dampen cheesecloth in cold water, wring it out, and line a sieve, folding the cloth into several layers. Put the yogurt into the sieve, tie the ends of the cloth together, and hang the bag on the handle of a wooden spoon set over a bowl. Put it in the refrigerator and allow it to stand all day or overnight, or even longer. The whey will drip out (this can be used for the liquid in bread baking) leaving the yogurt thick, with the texture of a soft, creamy cheese. The longer the yogurt hangs, the thicker the cheese will be. To serve, scrape the cheese away from the cloth, put it in a bowl, and season it with salt. Serve it plain or with olive oil drizzled over the top and a scattering of any of the herbal seasonings suggested below.
Store it covered in the refrigerator. The yogurt cheese will keep for at least 2 weeks.