Cook the linguine in a pan of boiling salted water, according to the packet instructions. Peel and finely slice the garlic, then finely slice the chilli. Pick and finely chop the parsley leaves, then finely slice the stalks. Put a large frying pan on a high heat and add a few good lugs of olive oil. Once hot, add the garlic, chilli, capers and parsley stalks. Cook for a couple of minutes, or until just starting to colour. Cut the herring into 2cm strips, then add to the pan and cook for 2 minutes. They will start to break up but don’t worry. Quarter and add the tomatoes and squeeze in the lemon juice. Use tongs to transfer the cooked linguine straight into the frying pan, bringing a little of the cooking water with it. Add the butter (if using), and toss everything together in the pan. Have a taste, season with sea salt and black pepper, add most of the parsley leaves and a lug of extra virgin olive oil. Mix again – use tongs if you need to – then transfer to a large platter. Scatter over the remaining parsley leaves and whack it in the centre of the table so everyone can tuck straight in.