The oil from a tin of anchovies is a powerhouse larder ingredient that you possibly never knew existed. It’s a flavour bomb that carries all the delicious flavour compounds of the fish themselves, especially if you want to add their wonderful flavour to a dish but want to save the anchovies to serve separately or as a garnish.This salsa verde is based on Giorgio Locatelli’s in his book Made in Italy, and it’s made with a knife rather than a blender. Chopping by hand gives it a much better texture, especially when you’re also using the stalks, which a blender can turn fibrous. The boiled egg is optional but traditional, and helps emulsify the sauce. Locatelli uses just the yolk, but I’ve used the whole egg, not least to avoid the faff of finding a use for the spare white. This sauce is incredible with lamb or mutton and very good with grilled fish.Anchovy oil salsa verdeWant to save this recipe? Download the Guardian Feast app to add this to your collection.Never throw fat down the sink. In fact, never throw fat away at all – it can be repurposed to use in cooking and is a wonderful ingredient in its own right that you never even knew you had. Anchovy oil specifically adds umami and a wonderful depth of flavour to a dish without overpowering it, and works brilliantly in salsa verde. (If need be, put the drained anchovies in a sterilised jar, top with extra-virgin olive oil – which can also be reused – seal and store in the fridge for up to two weeks.This is my first time adding boiled egg to the classic sauce, and I was really impressed with the results: it made a huge difference to the texture, and helped emulsify and fortify the sauce. It’s traditional to add just the hard-boiled egg yolk, but the whole egg, including the white, worked really well and disappeared into the salsa.100g flat-leaf parsley, leaves and stalks, or a mix of whatever soft herbs you have to hand1 small garlic clove, peeledSea salt and black pepper