Bring a large pot of salted water to boil. Cook spaghetti according to package directions until al dente. Reserve 1/2 cup pasta water before draining. 1 pound spaghetti.
While pasta cooks, in a large bowl whisk together ricotta, Parmesan, lemon zest, and lemon juice until smooth. 15 ounces whole milk ricotta cheese, 1/2 cup grated Parmesan cheese, 2 lemons.
In a large skillet over medium heat, warm olive oil and butter together. Add garlic and cook until fragrant, about 1 minute. 4 tablespoons olive oil, 2 tablespoons butter, 4 cloves garlic.
Add drained hot pasta to the skillet with garlic butter sauce. Toss to coat.
Add the ricotta mixture to the pasta, stirring until well combined.
Add pasta water a little at a time until sauce reaches desired consistency. (start with 1/2 cup water) 1 cup reserved pasta water.
Season with salt and pepper. 1/2 teaspoon salt, 1/4 teaspoon black pepper.
Serve immediately.
Notes
Pro Tip:
Slowly adding pasta cooking water while tossing helps the lemon ricotta mixture blend smoothly into a creamy sauce that coats the pasta perfectly. Start with a little and add more as needed to get the right consistency.