1. To make the breadcrumbs, whizz the sourdough in a food processor to make coarse crumbs. Heat the oil in a large frying pan over a medium heat. Add the anchovies and use a wooden spoon to break up the fillets, then tip in the chilli flakes and breadcrumbs, stirring until golden. Remove from the pan and set aside.
2. Cook the spaghetti in a large pan of salted boiling water, following pack instructions, until al dente. Meanwhile, warm the olive oil in a large frying pan over a low heat. Add the garlic and chilli and gently sizzle for 1 minute, until the garlic is fragrant and just lightly golden. Remove from the heat and leave to infuse in the pan.
3. Drain the spaghetti and toss in the frying pan with the garlicky oil, over a medium heat, until all the pasta is well coated. Season and serve immediately, scattered with the anchovy breadcrumbs and parsley