01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish.
02 - Bring a large pot of salted water to a boil. Add pasta and cook until al dente, 1-2 minutes less than package instructions. Drain and set aside.
03 - Steam or blanch broccoli florets for 2–3 minutes until they are bright green and slightly tender; drain and set aside.
04 - Melt butter in a large saucepan over medium heat. Add minced garlic and sauté for 1 minute until fragrant. Pour in heavy cream, bring to a gentle simmer, then whisk in 1 cup Parmesan until the sauce is thick and smooth. Season with salt, pepper, and nutmeg if using.
05 - In a large bowl, combine cooked pasta, chicken, broccoli, and Alfredo sauce. Mix until evenly coated.
06 - Transfer the mixture to the prepared baking dish. Sprinkle mozzarella and 1/4 cup Parmesan evenly over the top.
07 - Bake for 20–25 minutes until bubbly and golden on top.
08 - Let stand for 5 minutes before serving. Garnish with chopped parsley if desired.