Bring a large pot of salted water to a boil. Prepare 16 oz spaghetti according to the package instructions, cooking until al dente. In the final minutes of cooking, reserve 1 cup of the starchy pasta cooking water.
A few minutes before the pasta is ready, add 8 tbsps unsalted butter to a large skillet over medium heat. Heat the butter until it foams, then reduce the heat to low and add 4 tbsps lemon zest and 4 cloves garlic. Cook, stirring, for 1 to 2 minutes, or until fragrant. Remove from the heat if your pasta is still cooking.
When the pasta is al dente, use tongs to transfer it from the pot to the skillet with the butter mixture. Add 1/2 cup of the reserved pasta water and cook over low heat, tossing until a sauce forms and lightly coats the pasta. Add half the cheese and toss to incorporate. Add 2 tbsps lemon juice and the remaining half of the 1 cup Parmesan cheese and toss again, cooking until the sauce is smooth. If it becomes too thick or clumpy, add more pasta water as needed to loosen it.
Season to taste with salt, pepper and more lemon juice.
Garnish with more lemon zest and fresh parsley or basil leaves. Serve with more cheese.
