Peel and finely chop the onions and carrots. Trim the ends of the celery and finely chop them too. Slowly fry the onions, carrots and celery in some olive oil on low/medium heat until soft and golden but not browned. The low temperature is key in releasing the flavours. Take out of pan and set aside.
Now bring the pan to high heat and add the beef and pork mince. Stir often until the meat is browned. Reduce the heat and add the vegetables and red wine and continue to cook until the wine has reduced by half. Once the wine had reduced add half of the beef stock and a pinch of salt and black pepper. Stir and let the sauce simmer on low heat for 3 hours but remember to keep topping up with stock to stop it reducing too much.
Just before the ragu has finished, cook the tagliatelle in boiling salted water until al dente, then drain.
To serve add 3 to 4 large tablespoons of ragu into a mixing bowl and add (one portion) of the cooked tagliatelle pasta. Stir the pasta into the ragu, then plate the mixture and serve with Parmesan cheese.