01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish and set aside.
02 - Bring a large pot of salted water to a boil. Add pasta and cook until just al dente, 1-2 minutes less than package instructions. Drain and reserve.
03 - While the pasta cooks, steam or blanch broccoli florets for 2-3 minutes until vibrant green and just softened. Drain well.
04 - Melt butter in a large saucepan over medium heat. Add minced garlic and sauté for 1 minute until aromatic. Pour in heavy cream, bring to a low simmer, then whisk in Parmesan cheese until sauce is smooth and thickened. Season with salt, black pepper, and optionally, a pinch of nutmeg.
05 - In a large bowl, fold together the cooked pasta, diced chicken, blanched broccoli, and Alfredo sauce until everything is evenly coated.
06 - Transfer the mixture to the prepared baking dish. Distribute shredded mozzarella and the remaining grated Parmesan evenly over the top.
07 - Bake uncovered for 20-25 minutes until bubbling and golden brown across the surface.
08 - Let stand for 5 minutes before portioning. Garnish with chopped fresh parsley if desired.