Cook 6 medium potatoes in boiling salted water until tender. Drain, peel, cool, and dice. Place potatoes in a 9x13 greased baking dish. Melt ½ c butter add ½ c enriched flour. Add 4 cups milk and cook over low heat until thick, stirring constantly. Remove from heat. Add 1tsp salt, and 2 cups grated cheddar cheese. Stir until cheese melts. Pour sauce over potatoes. Sprinkle top with 2 cups grated cheddar. Bake at 375 for 25 minutes or until golden brown.