Preheat and prep: Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish. Bring a large pot of salted water to a boil.

Cook the pasta: Boil pasta until just shy of al dente, about 1–2 minutes less than package directions. During the last 2 minutes, add the broccoli florets to blanch. Drain well.

Start the sauce: In a large skillet or pot, melt butter over medium heat. Add garlic and cook 30–60 seconds until fragrant.

Build the roux: Sprinkle in flour, whisk, and cook 1–2 minutes until the mixture looks slightly golden. This keeps the sauce smooth.

Add liquids: Slowly whisk in chicken broth, then cream. Simmer gently, whisking, until thick enough to coat a spoon, 3–5 minutes. Don’t boil hard.

Season and cheese it: Stir in Parmesan, Italian seasoning, onion powder, nutmeg (if using), and a good pinch of salt and pepper. Taste and adjust. The sauce should be well-seasoned.

Combine: In a large bowl, mix pasta, broccoli, chicken, and the Alfredo sauce until everything is evenly coated.

Assemble: Spread the mixture in the baking dish. Top with mozzarella. For crunch, toss bread crumbs with a drizzle of olive oil and sprinkle over the cheese.

Bake: Bake 18–22 minutes, until bubbly around the edges and lightly golden on top. Broil 1–2 minutes at the end if you want extra color.

Rest and serve: Let it sit 5–10 minutes to set. Garnish with parsley and serve warm.