Step 1: Cook the Pasta: Cook the pasta according to package directions until al dente. Drain well and set aside.
Step 2: Cook the Chicken: In a large skillet, melt 2 tablespoons of butter over medium heat. Add the chicken pieces and cook until fully cooked and lightly browned, about 6-8 minutes. Remove the chicken from the skillet and set aside.
Step 3: Make the Alfredo Sauce: In the same skillet, melt the remaining 2 tablespoons of butter over medium heat. Add the minced garlic and saut for about 1 minute, until fragrant. Pour in the heavy cream and bring to a simmer. Stir in the Parmesan cheese, salt, pepper, and nutmeg (if using). Cook, stirring constantly, until the sauce has thickened slightly, about 3-5 minutes.
Step 4: Combine Ingredients: Add the cooked pasta and chicken to the skillet with the Alfredo sauce. Toss to coat evenly.
Step 5: Assemble the Casserole: Pour the pasta and chicken mixture into a greased 9x13 inch baking dish. Sprinkle the shredded mozzarella cheese evenly over the top.
Step 6: Bake: Bake in a preheated oven at 375F (190C) for 20-25 minutes, or until the cheese is melted and bubbly and the casserole is heated through.
Step 7: Garnish and Serve: Remove the casserole from the oven and let it cool for a few minutes before garnishing with fresh parsley. Serve hot.
Optional: For a richer flavor, consider adding a splash of white wine to the Alfredo sauce while it simmers. Vegetables like broccoli, spinach, or mushrooms can also be added to the casserole for extra nutrients and flavor.