Pour the broth or water and salt into a medium-size saucepan and bring to a boil. Lower the heat to medium-low and slowly whisk in the cornmeal. Cover, and cook, stirring frequently, until the polenta is soft and thick about 25-30 minutes. Remove the polenta from the heat, add butter (preferably porcini butter), parmesan, fontina, and black pepper; whisk until very smooth. Add a tablespoon of hot broth or water, if needed to thin out.