Slow cooker bolognese

Name: Slow cooker bolognese
Ingredients: 4 tbsp olive oil; 6 smoked bacon rashers, chopped; 1½kg lean minced beef (or use half beef, half pork mince); 4 onions, finely chopped; 3 carrots, finely chopped; 4 celery sticks, finely chopped; 8 garlic cloves, crushed; 500g mushrooms, sliced; 4 x 400g cans chopped tomatoes; 6 tbsp tomato purée; 2 tbsp dried mixed herbs; 2 bay leaves; large glass red wine (optional); 4 tbsp red wine vinegar; 1 tbsp sugar; cooked spaghetti, to serve; parmesan, to serve