press any exposed shells down into the liquid so they can cook evenly, but avoid heavy stirring.
Bring the mixture just up to a gentle simmer, then reduce the heat to low. Cover the Dutch oven with a lid and cook for 15 to 18 minutes, stirring once or twice during cooking to prevent sticking, until the pasta shells are tender and most of the liquid has thickened into a creamy sauce.
Remove the lid and check the consistency. If the sauce seems too thick, stir in a splash of beef broth or water, a tablespoon at a time, until it looks creamy and loose enough to coat the shells. If it’s too thin, let it simmer uncovered for 2 to 3 more minutes, stirring frequently, until slightly reduced.
Turn off the heat. Stir in the remaining 1/2 cup
