There are a lot of detailed steps. Don't let that freak you out. This is basically frying up the guanciale, seasoning with a little crushed chili, simmering some tomatoes, tossing some pasta in the sauce and adding cheese. It really is that easy. Easy weeknight cooking once you get it down.
Grab a big skillet. You will be tossing your pasta in the sauce so plan ahead.
Preheat your chosen skillet over medium heat.
Add the guanciale and cook, stirring frequently until you have beautiful little crispy pork bits. Remove the skillet from the heat.
Remove the pork bits with a slotted spoon and look at how much fat has rendered. You want about two tablespoons or so in the pan. Depending on how fatty your guanciale is you may have a little more or a lot more. Remove all but two tablespoons. Use a spoon and be careful. You are playing with hot fat in a hot pan. That's a pretty lethal combination.
Make sure your pot of water is at a rolling boil. I mean cranked. Salt your water. Now salt it some more. You want your water to taste like the sea.
Look at your spaghetti package. There will be a recommended cooking time on it. Set a timer for one minute less than the recommended cooking time and add your spaghetti to your pasta pot. As soon as you can get it all submerged start the timer.
Add the chili flakes and return the pan to the heat. Give the chili flakes a stir and cook for about 20 seconds then add in the tomatoes.
Scrape up any browned bits in the pan and simmer the sauce for 5 minutes or until your pasta timer goes off.
Toss the reserved crispy guanciale pork bits into the sauce. You can hold a few bits back to sprinkle over the amatriciana after you plate. Up to you.
Transfer the almost cooked pasta to the skillet along with about a 1/4 cup of the pasta cooking water. Toss to combine the pasta with the sauce and cook for about a minute.
Don't worry if it looks a little runny. The pecorino romano will fix that. Have faith.
Set a bit of cheese aside to garnish. Off heat, add half the pecorino. Toss to combine. Add the other half and toss again.
You don't want to wait to serve. Spaghetti all'amatriciana doesn't get better with age. Get it on the table!
Serve topped with a bit of pecorino romano and the reserved guanciale bits if you kept them. A little grind of black pepper is a nice touch.