Bring 1.75L (about 7.5 cups) of water to a boil. I know this is weirdly specific but we want really starchy water for the sauce. Trust me on this!
Once boiling add 1 tablespoon of salt and then cook your pasta in it according to package instructions. I mostly undercook dried pasta by a minute. Reserve a cup of the pasta water before draining.
When your pasta only has 5 minutes to go start the sauce.
Place the olive oil and sliced garlic in a large skillet cold then bring up to a gentle sizzle over a low-medium heat. This gives the olive oil time to be infused by the flavor of the garlic without burning.
The garlic should not color at all so turn the heat down if you need. When it has been sizzling for 1 - 2 mins add the red pepper flakes if using.
Add ½ cup of the pasta water and I like to use a whisk to really incorporate it. Whisk with your right hand and give the pan a good shake with your left.
Turn your heat up to medium if you need to get it simmering nicely.
Add the cooked, drained pasta and toss over and over to coat and thicken up. Let it gently bubble away together for 1 - 2 minutes. Add more pasta water if you need.
Toss the parsley through right before serving, season to taste and serve!
The video below will be really helpful!
It is no longer a traditional aglio e olio if you top with parmesan but I won't tell if you don't.