In a large pot or deep skillet, combine the uncooked spaghetti, chicken broth, water, minced garlic, salt, and black pepper.
Bring the mixture to a boil over medium-high heat, stirring occasionally to prevent the pasta from sticking.
Once boiling, reduce the heat to medium and continue cooking, stirring frequently, until the pasta is tender and most of the liquid has been absorbed, about 10 to 12 minutes.
Remove the pot from heat and immediately stir in the unsalted butter until melted and combined.
Add the freshly grated Parmesan cheese and stir until the cheese is fully melted and the sauce is creamy.
Sprinkle the chopped fresh parsley over the pasta and stir gently to combine.
Serve the pasta hot, garnished with extra Parmesan cheese if desired.