Ingredients

• 1 lemon
• 12 oz. spaghetti or other long pasta
• Kosher salt
• ¾ cup heavy cream
• 6 Tbsp. unsalted butter
• 3 oz. Parmesan, finely grated (about ¾ cup)
• Freshly ground black pepper

Instructions

1. Using a vegetable peeler, remove two (2"-long) strips of lemon zest. Thinly slice each strip lengthwise into strands; set aside for serving. Finely grate remaining zest into a large Dutch oven or other heavy pot. Cut lemon in half and squeeze juice into a small bowl to yield 2 Tbsp.; set aside.
2. Add cream to pot and cook over medium heat, whisking often, until liquid is just beginning to simmer, about 2 minutes. Reduce heat to medium-low. Whisk in butter 1 Tbsp. at a time until melted and sauce is creamy. Remove from heat; cover to keep warm.
3. Meanwhile, cook pasta in another large pot of boiling salted water, stirring occasionally, until very al dente, about 2 minutes less than package directions.
4. Scoop out ¾ cup pasta cooking liquid and add to cream sauce. Return sauce to medium heat. Using tongs, transfer pasta to sauce and cook, tossing often and adding Parmesan a little at a time, until sauce is creamy, about 3 minutes. If sauce looks tight, add 1–2 Tbsp. more pasta cooking liquid. (Cream sauces tighten as they cool, so lean on the saucy side.) Stir in reserved lemon juice; season with salt.
5. Divide pasta among bowls. Season with pepper and top with reserved lemon zest strands.