Bring a large pot of salted water to a boil. Use about 1 tablespoon of salt for every 4 quarts of water to enhance the pasta's flavor.

Add the spaghetti to the boiling water and cook according to package instructions until al dente, usually about 8-10 minutes.

Reserve 1 cup of pasta water, then drain the pasta in a colander. Do not rinse the pasta, as this removes the starch that helps the sauce adhere.

In a large skillet over medium heat, melt the butter. This will create a rich base for the sauce.

Add the minced garlic and red pepper flakes (if using) to the melted butter. Sauté for about 1-2 minutes until fragrant, being careful not to burn the garlic.

Stir in the lemon juice and lemon zest, mixing well to combine. The acidity of the lemon will brighten the flavors of the dish.

Add the cooked pasta to the skillet, tossing to coat it in the sauce. If the sauce is too thick, gradually add reserved pasta water until you reach your desired consistency.

Stir in the grated parmesan cheese, allowing it to melt and create a creamy texture. Season with salt and black pepper to taste.

Transfer the lemon butter pasta to serving plates. Garnish with chopped parsley and additional parmesan cheese if desired.

Serve immediately while hot, and enjoy the bright, buttery flavors!