Preparing the Ingredients

1. Asparagus: Wash and trim the tough ends of the asparagus spears. Cut the stalks into 1-inch pieces on a diagonal.
2. Lemon: Zest the lemon, avoiding the white pith. Juice the lemon.
3. Garlic: Mince the garlic cloves.
4. Walnuts (optional): If using, roughly chop the walnuts and toast them in a dry pan over medium heat until fragrant.

Making the Lemon Sauce

1. Heat olive oil: In a large skillet or pot, heat the olive oil over medium heat.
2. Sauté garlic: Add the minced garlic and cook for 30 seconds, or until fragrant. Be careful not to let it brown.
3. Add lemon zest and juice: Add the lemon zest and lemon juice to the skillet. Stir and cook for about 1 minute.
4. Season: Add salt and freshly ground black pepper to taste.

Cooking the Pasta and Asparagus

1. Cook the pasta: Bring a large pot of generously salted water to a rolling boil. Add the pasta and cook according to package directions, aiming for al dente (slightly firm).
2. Add asparagus: During the last 2-3 minutes of the pasta’s cooking time, add the asparagus pieces to the boiling pasta water.
3. Reserve pasta water: Before draining, scoop out about 1 cup of the starchy pasta water and set it aside.
4. Drain: Drain the pasta and asparagus together.

Combining Ingredients and Finishing Touches

1. Combine pasta and sauce: Immediately transfer the drained pasta and asparagus to the skillet with the lemon sauce.
2. Toss to coat: Toss everything together over medium heat, mixing thoroughly.
3. Add pasta water: Gradually add some of the reserved pasta water, a little at a time, until the sauce reaches a creamy consistency. The starch in the water helps create a silky texture.
4. Parmesan cheese: Remove the skillet from heat. Stir in the Parmesan cheese.
5. Walnuts (optional): If using, stir in the toasted walnuts.
6. Season and serve: Taste and adjust the seasoning with salt and pepper if needed. Serve immediately.