the liquid and adjust the seasoning if needed, keeping in mind the Parmesan will add saltiness as it bakes.
Slowly pour the cream-and-broth mixture over the pasta and peas in the ceramic baking dish, making sure the liquid seeps down through the shells. Gently nudge any exposed pasta down so most of it is at least partially submerged; a few pieces peeking out are fine and will brown slightly.
Cover the baking dish tightly with foil to trap in steam, which helps the shells cook evenly. Place the dish on the middle rack of the preheated oven.
Bake, covered, for 30 minutes. Carefully remove the foil (watch for steam) and check the pasta by stirring gently from the bottom. The shells should be mostly tender but may still have a slight bite, and the sauce will look loose at this stage.
