Get the Water Boiling: Fill a large pot with salted water and bring it to a rolling boil.
Cook the Pasta: Add the spaghetti to the boiling water and cook according to the package instructions. Remember, we want it al dente, with a slight bite.
Prepare the Garlic and Chilli: While the pasta cooks, finely mince the garlic and gather your red pepper flakes.
Create the Flavour Base: In a large skillet, heat the olive oil over medium heat. Add the minced garlic and cook until fragrant, but be careful not to burn it. This takes about a minute.
Add a Kick: Stir in the red pepper flakes and cook for a few seconds until fragrant.
The Magic Happens: About a minute before the pasta is finished cooking, reserve about half a cup of pasta water. Then, drain the pasta and add it directly to the skillet with the garlic and olive oil.
Toss and Emulsify: Toss the pasta vigorously in the skillet, letting the starchy pasta water create that dreamy sauce. If needed, add a splash more pasta water to achieve your desired consistency.
Season and Serve: Taste the pasta and adjust the seasoning with salt and pepper. Toss in the chopped parsley and a generous grating of Parmesan cheese (if using).
Divide and Conquer: Divide the spaghetti aglio e olio among plates and serve immediately.
