Bring a large saucepan of water to the boil and add the salt. Cut any hard rind from the guanciale and cut the meat into small batons. Finely grate the Pecorino. Separate the eggs, keeping all six yolks for the sauce; chill the whites for another use or freeze promptly.

Put the guanciale in a cold, wide frying pan. Cook over a medium-low heat for 8–10 minutes, stirring, until the fat has rendered and the pieces are golden and cooked. Turn the heat off. If there is a large pool of fat, spoon some into a heatproof bowl, leaving about 2 tablespoons in the pan.

Cook the spaghetti according to its packet until just al dente. While it cooks, whisk the yolks, 70 g of the Pecorino and the black pepper together in a large heatproof bowl. Gradually whisk in 3 tablespoons of warm pasta cooking water, added slowly so the yolks do not scramble.

Reserve a mug of pasta water, then drain the spaghetti. Toss it with the guanciale and its warm fat. Leave off the heat for 30 seconds, then transfer to the bowl of yolk mixture, tossing continuously with tongs.

Add small splashes of reserved pasta water and keep tossing until a glossy sauce coats the pasta. The bowl and pasta should be warm, with the egg gently thickened rather than scrambled; do not place the sauce over a strong direct heat. Divide between four warm bowls and finish with the remaining Pecorino. Serve immediately.