Add the water to a large pot along with the salt. When it reaches a boil, add the pasta and cook just under al dente (follow package directions for al dente and minus one minute).
As the pasta cooks, heat a large skillet over medium heat.
Add the olive oil, garlic and lemon zest, sauteeing until the garlic is fragrant and heated through.
Add the lemon juice and pasta water (dip a measuring cup into the pot once the pasta is almost done), whisking constantly.
Reduce the heat to medium low and add the cubes of butter one by one as you whisk continuously.
Once all the butter has been added and the sauce has emulsified, add the boiled pasta and toss it in the sauce gently until it's coated in the sauce.
Add the parmesan cheese and toss again.
Serve immediately with a sprinkle of freshly cracked black pepper, some more shaved parmesan, lemon zest and chopped parsley, if desired.