Boil the Water: Fill a large stockpot with water and add a generous pinch of Kosher salt. Bring to a rolling boil.
Cook the Pasta: Add the spaghetti to the boiling water. Cook for approximately 8 minutes (or according to package directions) until al dente. Important: Reserve 1 cup of starchy pasta water before draining.
Prep the Aromatics: While the pasta boils, thinly slice the garlic cloves into slivers and finely chop the fresh parsley.
Infuse the Oil: In a large skillet, combine the extra virgin olive oil and sliced garlic. Turn the heat to medium-low. Heating them together allows the garlic to infuse the oil without burning.
Add the Kick: Once the garlic is soft and slightly golden, stir in the red pepper flakes.
Create the Emulsion: Pour about 1/2 cup of the reserved pasta water into the skillet with the oil and garlic. Whisk or stir vigorously over medium heat until the liquid bubbles and turns into a glossy, thickened sauce.
The Final Toss: Add the drained spaghetti and fresh parsley to the skillet. Toss continuously with tongs for 1–2 minutes, adding more pasta water if needed, until the sauce clings perfectly to the noodles.
Season and Serve: Taste and add a final pinch of salt if necessary. Serve immediately in warm bowls, topped with optional Parmesan cheese.