In a large deep skillet or wide saucepan, combine the uncooked spaghetti, vegetable broth, water, lemon juice, lemon zest, 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 to cook, stirring frequently, until the pasta is al dente and most of the liquid has been absorbed, about 10 to 12 minutes.
Lower the heat to medium-low and stir in the heavy cream, unsalted butter, and grated Parmesan cheese until the sauce is creamy and well combined.
Cook for an additional 2 to 3 minutes, stirring constantly, until the sauce thickens slightly and coats the pasta.
Remove the skillet from heat and stir in the chopped fresh parsley.
Taste and adjust seasoning with additional salt, pepper, or lemon juice if desired.
Serve immediately, garnished with extra Parmesan and parsley if preferred.