Pre-Cooked Corn Meal  with Porcini Mushrooms. Ideal for a quick fix for dinner or a shortcut in a recipe. Fry onion, celery, carrot, garlic, salt and pepper in oil, add the tomato and cook for 15 minutes. Boil 62.6 fl oz of water in a saucepan with a pinch of salt. Add 10.5 oz of polenta to boiling water and stir continuously, after 5 minutes the polenta is ready. Pour the prepared sauce onto a plate, add the polenta and pour more sauce on top.