Peel, quarter and slice the red onion, slice the chillies and finely grate the garlic. Roughly chop the anchovies

Add 100ml of the olive oil to a pan over a medium heat. Once hot, add the sliced onion with a pinch of salt and cook briefly. Add the garlic and cook for a couple of minutes, then add the chillies. Cook for a minute or 2, then remove from the heat

Add the anchovies, stirring vigorously to 'melt' them into the sauce, then add the capers. Zest the orange into the sauce, then add half of its juice 

Stir in the vinegar, then roughly chop the parsley and add it in too. Pour in the remaining 100ml of olive oil, then taste to check you're happy with the seasoning. At this point, the sauce really benefits from an hour or 2 of resting, but it can be used right away

When ready to serve, bring a large pan of salted water (at least 2 litres) to the boil. If you're using dried spaghetti, cook it according to the packet instructions, or to your preferred level of al dente. If you're using fresh, cook it for 2-3 minutes

When the pasta cooking water has started to become starchy (around 7 minutes for dried pasta, around 2 minutes for fresh), carefully remove a small mugful of pasta water. Put the sauce back over a medium heat. Add approximately half a mug (around 100ml) of the water to the sauce and swirl around to integrate, allowing it to simmer gently while the pasta finishes cooking

Drain the spaghetti, add to the sauce, turn the heat up and swirl around with tongs so the pasta is rolling through the sauce. After a minute at the boil the sauce should become rich and velvety with the pasta and sauce becoming one wonderful, glazed mass of goodness. Carefully transfer to warm bowls and serve immediately