Cook the pasta according to package directions until al dente. Drain and set aside.

In a large saucepan over medium heat, melt the butter. Stir in the flour and whisk for 2–3 minutes to form a smooth base.

Add the garlic, heavy cream, salt, and white pepper. Stir in 1 cup of Parmesan cheese. Cook, stirring often, until the sauce thickens, about 8–10 minutes.

Remove from heat and stir in the mozzarella and cream cheese until fully melted and smooth. Adjust seasoning if needed.

Combine the cooked pasta, diced chicken, and sauce in a large pot, mixing well.

Transfer the mixture to a 9×13-inch baking dish and sprinkle the remaining Parmesan over the top.

Bake at 350°F for 20–25 minutes, or until the sauce is bubbly and the top begins to lightly brown. Garnish with parsley if desired.