In a medium, heavy-bottomed saucepan, bring the water to a boil. Add the salt. Then add the polenta to the pot slowly, whisking constantly. Reduce the heat to low and cook COVERED, stirring often, until the mixture thickens and the cornmeal is tender, about 20 minutes. The polenta can be eaten now, but the flavors develop more and you’ll lose some of the grittiness if you can allow it to simmer another 20-30 minutes. Not essential, though.Stir in the butter and cheese and serve immediately or keep warm in a bowl set over a saucepan of simmering water. Polenta should be pourable and creamy. If it’s too thick, stir in more liquid.