01 - Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish.
02 - Cook the pasta in a large pot of salted boiling water until al dente. Add broccoli florets during the last 2 minutes of cooking. Drain and set aside.
03 - In a large skillet over medium heat, melt butter. Add garlic and sauté for 1 minute until fragrant.
04 - Stir in heavy cream and bring to a gentle simmer. Add 1 cup Parmesan and ½ cup mozzarella cheese, stirring until melted and smooth. Season with salt, pepper, and nutmeg.
05 - In a large mixing bowl, combine cooked pasta, broccoli, chicken, and Alfredo sauce. Mix well to coat evenly.
06 - Transfer mixture to the prepared baking dish. Sprinkle remaining ½ cup mozzarella and ½ cup Parmesan evenly over the top.
07 - Bake uncovered for 20 minutes, or until bubbly and golden brown on top.
08 - Let rest 5 minutes before garnishing with parsley and serving.