01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with nonstick cooking spray or oil.
02 - In a mixing bowl, combine the softened butter, minced garlic, parsley, dill, lemon juice, salt, and pepper. Mix thoroughly until all ingredients are evenly incorporated. Set aside.
03 - Distribute the chicken pieces in an even layer across the bottom of the prepared baking dish.
04 - Spoon dollops of the garlic-herb butter mixture over the chicken pieces, spacing them evenly.
05 - Pour the heavy cream and chicken broth evenly over the chicken. Sprinkle the grated Parmesan cheese on top.
06 - Sprinkle shredded mozzarella cheese evenly over the casserole for an optional extra cheesy layer.
07 - In a small bowl, combine the panko breadcrumbs with melted butter and dried thyme or parsley. Sprinkle the mixture evenly over the entire surface of the casserole.
08 - Bake for 30 to 35 minutes, until the topping is golden brown and the chicken is cooked through to an internal temperature of 165°F.
09 - Remove from the oven and let the casserole rest for 5 minutes before serving to allow the sauce to set.