Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package directions until al dente. Before draining, reserve about 1 cup of pasta water.

While pasta cooks, heat olive oil in a large skillet over medium-low heat. Add minced garlic and red pepper flakes (if using) and sauté for 1-2 minutes until fragrant. Be careful not to burn the garlic.

Drain the pasta and add it directly to the skillet with the garlic oil. Add the grated Parmesan cheese and about 0.25 cup of the reserved pasta water. Toss well to combine, adding more pasta water a tablespoon at a time if needed, until a light sauce forms and coats the pasta.

Season with salt and freshly ground black pepper to taste. Garnish with fresh chopped parsley and serve immediately.