Drizzle the olive oil evenly over the pasta and the top of the Boursin. Sprinkle the kosher salt over everything.
Carefully pour the broth into the dish, aiming around the edges and between the pasta rather than directly on top of the cheese. The liquid should come up around the pasta but not completely submerge the Boursin.
Cover the ceramic baking dish tightly with foil to trap in the steam. Place it on the middle rack of the preheated oven.
Bake for 25 minutes, then carefully remove the foil (watch for steam). Stir the pasta gently, pulling some of the softened Boursin into the liquid to start forming a sauce.
Return the dish to the oven, uncovered, and bake for another 10–15 minutes, stirring once halfway through, until the pasta is tender and most of the liquid has turned into a creamy sauce.
Take the dish out of the oven and give everything a thorough stir, breaking up any remaining chunks of Boursin until the sauce is smooth and coats the fusilli. Taste and adjust the seasoning with a little more salt if needed.
Let the pasta sit for 3–5 minutes to thicken slightly, then serve straight from the baking dish while it’s warm and extra creamy.
For extra protein, stir in 1–2 cups of cooked shredded rotisserie chicken, sliced Italian sausage, or drained canned chickpeas when you uncover the dish for the final 10–15 minutes of baking. To sneak in more veggies, add a couple of handfuls of baby spinach or chopped kale right after baking and stir until wilted, or toss in halved cherry tomatoes or frozen peas during the last 10 minutes in the oven. If you like a little kick, sprinkle in red pepper flakes or cracked black pepper before baking. You can also swap the broth for a mix of half broth and half milk for an even richer sauce (just keep an eye on it so it doesn’t boil too vigorously). Any short, curly pasta shape—like rotini or cavatappi—can stand in for fusilli if that’s what you have in the pantry. For make-ahead prep, assemble the dish earlier in the day, cover, and refrigerate; when you’re ready, add a splash more broth and bake, adding a few extra minutes to the covered time if it goes into the oven cold.
