Bring 4 cups of salted water to the boil in a saucepan. Pour in the cornmeal and whisk for about 5 minutes until it cooks.
Remove from the fire and transfer to a bowl. Add the butter and cheese, mix well, then add the beaten egg and season with salt and pepper ( by now it should set and almost solid). Set aside. In a large pan gently fry the onion in the oil and when it softens, add the skinned sausages cut into pieces. Stir for a couple of minutes, then pour the tomato polpa over. Simmer for around 20 minutes.
In the meantime, with your wet hands, form small polenta balls and add to the sauce. Cook for a futher few minutes on a VERY LOW FLAME. Add the chopped parsely just before serving.