Begin by bringing a generously salted pot of water to a rolling boil. Add the pasta and follow the instructions on the package for cooking time. Before draining, remember to save at least 1/2 cup of the pasta cooking water.
In a pan, sauté the thinly sliced garlic in olive oil over medium-high heat for about a minute.
Pour in ½ cup of the reserved pasta water, then add the cooked spaghetti, chili flakes, and season with salt and black pepper.
Introduce the chopped parsley and grated Parmesan, and gently combine everything over low heat for 2-3 minutes.
Serve, garnished with extra Parmesan and parsley as desired.
