Melt butter in a large saucepan over medium heat. Stir in flour, and cook, stirring constantly, 2 to 3 minutes or until flour is lightly browned. Whisk milk into butter mixture; bring to a boil. Reduce heat, and simmer 6 minutes or until thickened. Stir in cheese and next 3 ingredients; stir until cheese melts.
Spread 1/4 cup cheese sauce in a 13- x 9-inch baking dish coated with cooking spray. Layer half of potatoes over sauce; top with half of cheese sauce. Repeat with remaining potatoes and cheese sauce. Bake at 325°, covered with aluminum foil, 1 1/2 to 2 hours.
Combine breadcrumbs and remaining ingredients in a small bowl; spread evenly over potatoes. Bake, uncovered, 20 to 30 minutes or until potatoes are tender. Garnish if desired.