In a large pan or casserole, add the butter, tomatoes and tomato purée and place on a low heat.
Chop an onion in half and peel the papery skin away, trim the top and the roots, but don’t cut away the whole root structure.
Put the two onion halves into the pan and bring to a simmer.
Heat for half an hour to forty minutes, until the sauce is thick and rich.
Put a large pan of salty water on to boil and cook the spaghetti according to the packet instructions.
While the pasta is cooking, use an immersion blender to whizz up the onion, which is now soft and cooked, into the sauce.
Once cooked, drain the spaghetti and add into the sauce, briefly heating while you mix. Serve onto four plates, with burrata and basil on top if you like.
