Preheat oven to 350°. Spray a 2-quart baking dish with nonstick cooking spray.
Peel and thinly slice potatoes.
In a large nonstick saucepan, melt 1/4 cup butter over medium heat. Sift flour over butter, whisking to combine. Cook flour mixture for 2 to 3 minutes or until thickened, whisking well. Slowly add milk, whisking to combine. Cook for 5 minutes or until thickened, whisking frequently. Add 3/4 teaspoon salt and 3/4 teaspoon pepper, whisking well.
Spread 1/4 cup milk mixture over bottom of prepared dish. Layer half of potatoes evenly in a circular pattern over milk mixture. Spread half of remaining milk mixture over potatoes. Top with 1 tablespoon chopped chives and 1/2 cup grated Parmesan cheese. Repeat layers with remaining potatoes, milk mixture, and 1 tablespoon chopped chives.
Microwave remaining 2 tablespoons butter in a microwave-safe bowl for 30 seconds or until melted. Combine butter, panko, remaining 1/2 cup grated Parmesan, remaining ¼ teaspoon salt, and remaining 1/4 teaspoon pepper in a medium bowl. Spread over potatoes. Cover, and bake for 45 minutes. Remove cover, and bake for 15 minutes or until golden brown. Top with remaining 1 tablespoon chives. Let stand for 10 minutes before serving.