Cut the garlic into thin slices.
Roughly chop the anchovies and olives and crush the capers.
Heat the olive oil and add the garlic.
Cook the garlic very gently until just beginning to colour, then add the anchovies and stir to dissolve.
Stir in the chilli flakes, then the olives and capers, and turn up the heat slightly until you can hear them sizzling.
Add the passata and stir well, then simmer vigorously for about five minutes, or until the pasta is done.
Check the seasoning.
Cook the spaghetti and add to the sauce being sure to add a ladle of the cooked pasta water. The salty, starchy water not only adds flavor but helps glue the pasta and sauce together; it will also help thicken the sauce.