In a heavy saucepan bring water and salt to a boil and gradually whisk in polenta in a thin stream. Cook polenta over moderately low heat (it should be barely boiling), stirring constantly, until very thick and pulls away from side of pan, about 20-30 minutes. Remove pan from heat and cover to keep warm. Stir polenta just before using. Polenta will keep warm, covered, about 20 minutes.
You can stir in parmesan, cheddar or goat cheese for added richness.