Cook pasta – Bring 4 litres (4 quarts) of water to the boil with the salt. Add pasta and cook per the packet directions.
Reserve pasta water – Just before draining, scoop out 1 cup of pasta cooking water, then drain the pasta.
4 Cook guanciale – While the pasta is cooking, place guanciale in a non stick pan over medium high heat. Cook for 4 to 5 minutes until golden. No oil needed – as the guanciale heats up, the fat will melt so it fries in its own fat. If using garlic, add it in the last minute.
5 Pasta in pan – Tip the hot pasta into the pan and toss to coat in guanciale fat.
Mix pasta in sauce – Transfer the pasta and any residual fat in the pan into the bowl with the egg.
6 Add 1/2 cup (125 ml) pasta cooking water. Stir vigorously using the handle of a wooden spoon for 1 minute and watch as the sauce transforms from watery to creamy and clings to the pasta strands!
7 Serve – Transfer into warm bowls. Serve immediately, garnished with a little extra parmigiana reggiano if desired, and a pinch of black pepper and finely chopped parsley.