01 - Bring a large pot of generously salted water to a rolling boil. Cook the pasta according to package directions until al dente. Reserve approximately 240 ml (1 cup) of the pasta cooking water, then drain the pasta thoroughly.
02 - Concurrently, in a large skillet set over medium heat, melt the unsalted butter. Add the minced garlic and sauté for 1 to 2 minutes until fragrant, ensuring it does not brown.
03 - Incorporate the crushed red pepper flakes (if using), freshly ground black pepper, and salt into the skillet.
04 - Add the drained pasta to the skillet with the garlic butter. Toss to ensure the pasta is evenly coated. Gradually stir in small amounts of the reserved pasta water as needed to emulsify and achieve a glossy sauce that clings to the noodles.
05 - Remove the skillet from the heat. Add the grated Parmesan cheese and chopped fresh parsley, tossing vigorously until the cheese is melted and the noodles are well-coated and glossy. If desired, incorporate the lemon zest for an added layer of brightness.
06 - Taste and adjust seasoning as necessary. Serve immediately, garnished with additional grated Parmesan cheese.