Cook potatoes, withdrawn, drained and cut into 2. In a pan heat 2 tbsp olive oil or sunflower oil and fry the potatoes until golden, then remove to a plate. Liver is divided into four, sprinkle both sides with salt and pepper. In a pan melt the butter and fry the liver on both sides and leave in a warm place. In a pan pour the remaining olive oil and fry chopped bacon, onion and garlic until golden brown. Add tomatoes, thyme and tomato sauce. Allow to boil, reduce heat and stew 4-5 minutes. Add the potatoes, stir, put on a layer of liver, quickly replace the lid and stew for 3-4 minutes. Season with pepper and sprinkle with parsley.