Spaghetti alla Carbonara

Variations

• Guanciale → pancetta/bacon: Easier to find; the flavor comes out a touch milder.
• Cacio e pepe: Skip the egg — just pecorino and pepper.
• Amatriciana: Same guanciale, but a red sauce with tomato added.
• Yolks only: Drop the whole egg for a richer, thicker sauce.

Tips

• A yolk emulsifies below the temperature at which the same yolk sets, and the gap between those two is the whole dish. Why sauces split ranks egg yolk's lecithin as the most powerful emulsifier and names this dish, and a few lines later says egg-based sauces coagulate above about 70°C — "make carbonara over a live flame and you get scrambled eggs, not sauce." Those are two faces of one ingredient. Emulsifying happens under that number and setting happens over it, so the entire method is keeping the pan below it.
• The pasta water is what holds that window open. Cooking noodles calls the starch dissolved in it an emulsifier between fat and water, and cooking eggs adds the second half: starch granules swollen at 60-75°C get between the egg proteins and lift the setting temperature by tens of degrees. Two or three tablespoons cools the pan and raises the ceiling at the same time. That is why it goes in a little at a time rather than all at once.
• Carbonara is cacio e pepe with a yolk added. Fettuccine alfredo lines the pastas up by what holds the sauce together — cacio e pepe on starch alone, carbonara adding egg yolk, aglio e olio on oil, alfredo on butter — and notes that the guide's ranking is "why carbonara forgives more than cacio e pepe does". That is the case for leaving cream out: not that cream is forbidden, but that it is simply an easier emulsifier, and using it removes the thing the dish exists to demonstrate.
• Pecorino is a supplier of fat, not only of flavour. Dairy and heat says a long-aged hard cheese does not stretch but releases its fat readily, and gives the fix for a clumping cheese sauce as lower heat plus a little starch. Carbonara is that prescription written out as a recipe. It is also why the cheese must be grated very finely: coarse shreds clump before they melt.
• Start the guanciale in a cold pan. Dropped into a hot one, the outside firms first and locks the fat inside. Brought up slowly it gives all of it up, and that rendered fat is one of the three things being emulsified while what is left of the meat crisps in it.
• No cream. Real carbonara gets its silkiness from egg yolks, cheese, and pasta water alone.
• Take it off the heat before adding the eggs so they emulsify instead of scrambling.
• Pasta water is key — its starch emulsifies the sauce. Save some before draining.
• Pecorino Romano is the classic cheese. It's salty, so go light on the pasta-water salt.
• Use plenty of freshly cracked black pepper — some say it's the source of the name 'carbonara' (charcoal).