This pasta cooks right in the sauce (instead of separately in boiling water), so it absorbs lots of flavor—and there’s fewer dishes to wash!
Add sausage, onion, salt, pepper, and pepper flakes (if using) to Dutch oven. Use wooden spoon to break sausage into small pieces. Cook over medium-high heat, stirring occasionally and continuing to break up sausage, until sausage is lightly browned and dark brown bits have formed on bottom of pot, 10 to 12 minutes.
Carefully add ½ cup chicken broth and use wooden spoon to scrape up browned bits on bottom of pot. Cook until liquid has mostly evaporated, about 2 minutes.
Stir in pasta and remaining 3½ cups broth. Bring mixture to boil.
Reduce heat to medium-low and cover pot with lid. Cook until pasta is tender, 10 to 12 minutes. (Some liquid will remain in pot.) Turn off heat.
Use oven mitts to remove lid. Add peas, Parmesan, lemon zest, and lemon juice. Use wooden spoon to stir vigorously for 1 minute. Let sit, uncovered, for 5 minutes to allow peas to warm through and sauce to thicken slightly. (Sauce will continue to thicken as pasta cools.)
This recipe uses just one pot to cook the pasta AND the sauce together, no draining a separate pot of boiling water required! This is possible not through magic, but through the precise measurement of the liquid needed to cook your pasta. There is JUST enough broth for the pasta to absorb and become tender, plus a little extra to create the sauce. And that sauce takes shape when you stir the pasta—hard!—after it finishes cooking. The pasta releases starch as it cooks, helping the liquid thicken into a creamy (creamless!) sauce.