Put water for pasta on to boil, though you don't need to get started on the sauce until it is pretty well boiling.
Pour the oil into a wide, shallowish frying pan, casserole or wok, and put on a medium heat.
Add the finely chopped anchovies and cook for about three minutes, pressing and pushing with a wooden spoon, until the anchovies have almost "melted", then add the garlic and chilli flakes (or sliced then diced jalapenos) and cook, stirring for another minute.
This is probably the stage at which you will want to be salting the boiling pasta water and adding the spaghetti to cook according to packet instructions.
Going back to the sauce, add the tomatoes, olives and capers and cook for about ten minutes, stirring every now and again, by which time it will have thickened slightly. Taste for seasoning.
Just before the pasta is ready, remove about an espresso cupful of cooking water, and reserve it. When the pasta is cooked as desired, drain and add the spaghetti to the sauce in your wok or pan, adding a little reserved pasta water, if needed, to help amalgamate the sauce. Scatter with chopped parsley.
Recipe from Nigella: Kitchen by Nigella Lawson (published by Chatto & Windus).