01 - Preheat your oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - In a large pot of salted boiling water, cook the pasta until al dente according to package directions. During the final 2 minutes of cooking, add the broccoli florets to the pot. Drain thoroughly and set aside.
03 - In a large skillet over medium heat, melt the unsalted butter. Add the minced garlic and sauté for approximately 1 minute until fragrant.
04 - Pour the heavy cream into the skillet and bring to a gentle simmer. Stir in 1 cup of Parmesan cheese and ½ cup of mozzarella cheese, stirring continuously until the cheeses are melted and the sauce is smooth. Season with salt, black pepper, and nutmeg if desired.
05 - In a spacious mixing bowl, combine the cooked pasta, broccoli, diced chicken, and the prepared Alfredo sauce. Mix thoroughly to ensure all ingredients are evenly coated.
06 - Transfer the mixture to the prepared 9x13-inch baking dish. Evenly sprinkle the remaining ½ cup of mozzarella cheese and the remaining ½ cup of Parmesan cheese over the top.
07 - Bake uncovered for 20 minutes, or until the dish is bubbly and the cheese topping is golden brown.
08 - Allow the baked dish to rest for 5 minutes before garnishing with fresh parsley, if using, and serving hot.