Heat the butter and oil in a pan and sweat the onions and carrot until soft (about 10 minutes).
Increase the heat and add the minced beef.
Fry for a few minutes, then stir, cooking until meat is browned all over.
Add the tomato purée, tinned tomatoes, salt and pepper to taste, and the stock.
Simmer gently for about ¾ hr, until the mixture thickens, stirring occasionally.
Add 2 tbsp sherry and cook for a further 5 minutes.
Meanwhile, place the spaghetti in lots of boiling salted water and cook according to their instructions.
Drain.
Serve with Bolognese sauce on top and sprinkle with freshly grated parmesan cheese.