In a large, heavy-based pan, fry the bacon in 2 tbsp of the olive oil. When the bacon is crispy and has released some natural fats, add the onion, celery, carrot, garlic, thyme, bay leaf and oregano and cook over a medium heat until the vegetables have softened and taken on a little colour.
Add the canned tomatoes, the tomato purée, anchovy essence and Worcestershire sauce. Stir to combine.
Meanwhile, in a large frying pan, heat another 2 tbsp of the olive oil and fry the mince in small batches until browned. While the meat is frying, break up any lumps with the back of a wooden spoon. Repeat until all the mince is browned. Drain off any fat and add to the tomato mixture.
Add 2 tbsp of the oil to the same frying pan, fry the chicken livers until brown and crusty and add the livers to the meat. Deglaze the frying pan with some of the red wine, scraping any crusty bits from the bottom. Pour this wine, the remaining wine and the stock into the tomato and meat mixture. Bring to the boil, reduce the heat and simmer, stirring from time to time, for about 2 hours. Season to taste. If the liquid reduces too much, top up with water. When the meat is tender allow to cool, then chill.
When cold, lift off the solidified fat and discard.
Cook the spaghetti in plenty of boiling water with the remaining olive oil and heat the sauce. When the pasta is cooked and the sauce heated through, divide the pasta among six dishes and serve the sauce on top.