In a saucepan, melt butter over low heat. Stir in flour until smooth. Gradually
add milk; cook and stir over medium heat until mixture thickens. Remove from heat
and add salt and cheeses. Stir until Cheddar cheese melts.
Place potatoes in a greased
2-quart baking dish and add cheese mixture, stirring gently to mix. Sprinkle bread
crumbs on top.
Bake uncovered at 350 degrees F for 30 to 35 minutes.