PREPARE: Use a small, sharp knife to trim the tenderloin of any silver skin, then pat dry. Whisk together the spice rub ingredients, then rub evenly over the pork, making sure it is well covered. Set aside.

MAKE THE SALSA VERDE: Heat the oven to 200°C / 400°F / Gas 6. Meanwhile, make the salsa verde by finely dicing the parsley, red onion and garlic (you can use a food processor to pulse these ingredients together, but leave them chunky, rather than a paste). Transfer to a bowl and stir through the vinegar, olive oil, sea salt and chilli flakes, taste and adjust seasoning as necessary.

COOK THE MEAT: Heat the butter and oil in a large, ovenproof frying pan (see note). When the butter is hot and foaming, brown the tenderloin well on all sides. This should take 5-6 minutes. Transfer the pan to the oven for 12-15 minutes until the pork is cooked through. If you have a digital thermometer, you can check that the thickest part of the meat registers at least 65°C / 150°F, though you can take it up to 70°C / 158°C if you prefer your meat more well done.

REST THE MEAT: Remove the pork from the oven, cover loosely with foil and keep warm for 5 minutes. When the pork has rested, slice thickly and generously spoon the salsa verde over the top.

ROAST POTATO INSTRUCTIONS: I like to serve this pork with roast potatoes - as my oven is a little smaller I use the fan-bake setting on 180°C / 350°F and place cubed potatoes and chopped rosemary tossed in a little olive oil on a lower shelf for 25-30 minutes before I put the pork in the oven.