Step 1 In a small pot, bring the water to a simmer. Slowly rain in the cornmeal, whisking to avoid any lumps. Whisk in the salt. Cook, stirring frequently, until the polenta is softened and fluffy, 20 to 30 minutes (timing will vary depending on grind and brand). The polenta should be very thick, but if it dries too much before it is softened, whisk in additional water as needed. When the polenta is ready, whisk in the butter. Remove from heat. Spread and smooth the polenta into a plastic wrap-lined and greased baking dish or pan, so the polenta is approximately ¾-inch thick. Loosely cover and refrigerate until cold and firm. The polenta can be made up to two days in advance.