Bring a large pot of salted water to a boil in a Dutch oven or large pot. Add 1 pound dried spaghetti and cook according to package directions for al dente. Reserve 1 1/2 cups of the pasta water. Drain the pasta.
Heat 1 tablespoon olive oil in the same Dutch oven over medium heat until shimmering. Add 1 bunch chopped asparagus, 4 minced garlic cloves, 1/2 teaspoon of the kosher salt, and 1/4 teaspoon black pepper. Cook until the asparagus is bright green and crisp-tender, 1 to 3 minutes. Remove the Dutch oven from the heat.
Add 1 (about 15-ounce) container whole-milk ricotta cheese, 1 cup of the reserved pasta water, 2 ounces finely grated Parmesan cheese, the finely grated zest of 1 medium lemon, 3 tablespoons lemon juice, and the remaining 1/2 teaspoon kosher salt. Stir until the ricotta is melted and the sauce is creamy.
Add the spaghetti and toss to coat. If you'd like a thinner sauce, toss in more pasta water a few tablespoons at a time. Taste and season with more kosher salt as needed. Garnish with more grated Parmesan cheese, freshly ground black pepper, and lemon zest if desired.
Recipe Notes