Bring a large pot of salted water to a boil. Add the spaghetti and cook until just shy of al dente—about one minute less than the package directions.
A few minutes after the pasta goes in, heat olive oil in a large sauté pan over medium heat. Add the sliced garlic and red pepper flakes, cooking for 3 to 5 minutes until the garlic is lightly golden and fragrant.
Once the pasta is ready, use tongs to transfer it straight into the sauté pan, along with about ½ cup of the starchy pasta water. Toss everything together until the noodles are well coated in the garlicky oil. If the sauce seems dry, add a bit more pasta water—start with another ¼ cup.
Finish with a generous handful of chopped parsley, toss again, and serve right away while it’s still hot and glistening.
