Bring a large saucepan of salted water to a boil and get all of the sauce ingredients ready, so that you can make the sauce while the pasta is cooking.
To cook the breadcrumbs, heat the olive oil and butter in a frying pan. Add the breadcrumbs, chilli flakes, lemon zest and salt and cook for a few minutes, stirring often, until the breadcrumbs have turned golden brown. Tip out onto a small plate or bowl while you cook the pasta and sauce.
Cook the spaghetti for 1 minute less than the packet instructions, then drain and reserve a ladle full of the cooking water.
While the spaghetti is cooking, heat the oil and butter in a large frying pan over a low heat. Add the onion and cook for 5 minutes, until softened but not coloured. Add in the garlic and cook for 1 minute more, then add in the salt and pepper, clams and wine. Cover the pan with the lid and leave for 3 minutes, at which point the clam shells should all be open - discard any that haven’t opened.
If the sauce is quite liquid, scoop out the clams and reduce the sauce for a few minutes, then add the clams back into the pan. Add the chopped parsley, drained spaghetti and a ladleful of pasta water. Turn the heat up high and stir the ingredients together then divide between four serving dishes or serve on a large platter, topped with the toasted breadcrumbs.