1. Toast the walnuts. Preheat oven to 325°F. Spread walnuts out on a small sheet tray. Bake on the center rack of the preheated oven for 8-10 minutes, until golden brown and fragrant. Transfer to a wire rack to cool completely before adding to pesto.

2. Get prepped. While walnuts toast, gather all ingredients. Remove sausage from its casing. Separate basil leaves from the stems.  Fill a large pot with water for cooking the pasta and bring to a boil. Place a large skillet on the stovetop for cooking the sausage. Take out a food processor or blender to prepare the pesto.

3. Brown the sausage. Heat the skillet over medium-high heat. Add 1 tablespoon olive oil to the pan. Add sausage to pan in small chunks. Cook undisturbed for about 4-5 minutes, until well-browned on bottom. Turn and break into smaller pieces. Cook 2-3 more minutes, until golden brown and cooked through. Remove pan from heat, leaving sausage in pan.

4. Make the pesto. While the sausage cooks, add basil, 4 tablespoons olive oil, walnuts, garlic and parmesan into a food processor and blend until smooth. Season with salt and pepper to taste. Set aside.

5. Cook pasta. Season boiling pasta water generously with salt (about 1-2 tablespoons of kosher salt per 4-6 quarts of water). Cook pasta 1-2 minutes short of al dente. Drain, reserving 1 cup of pasta water.

6. Finish the dish. Warm pan with sausage over medium-high heat until sausage comes back to a sizzle. Add in cooked pasta and toss to combine. Turn off heat, and stir in pesto and ricotta cheese. Add about ¼ cup of reserved pasta water, or more as needed, to loosen the sauce. Taste for seasoning. To serve, spoon the pasta into serving bowls and top with Parmesan and lemon zest, as desired. Enjoy!