Heat 1 tablespoon of the oil in a large frying pan over a medium heat. Add the chopped onion, carrot and celery and cook for 5-7 minutes, until starting to soften.
Add the minced garlic and cook for a minute, then tip in to the slow cooker.
Using the same frying pan, add the ½ tablespoon oil and turn the heat up to high. Cook the ground beef until browned, breaking it up with a wooden spoon as it cooks.
Add the tomato puree / tomato paste to the beef and cook for a minute, then tip into the slow cooker.
Add the wine to the frying pan and scrape the bits off the pan, then pour this into the slow cooker together with the tomatoes, dried oregano, thyme, bay leaves, Worcestershire sauce and salt and pepper.
Place the lid on the slow cooker and cook on LOW for 8 hours.
Serve with cooked spaghetti, sprinkle with grated parmesan and chopped parsley, optional.
Leftover bolognese will keep in the fridge, covered, for up to 3 days. Or freeze for up to 3 months.