Preheat oven to 350°F. and butter a 2-quart shallow baking dish. In a heavy saucepan melt butter over moderately low heat and whisk in flour. Cook roux, whisking, 3 minutes and add broth in a stream, whisking. Bring sauce to a boil, whisking, and simmer, whisking, until thickened, about 2 minutes. Remove pan from heat and whisk in cheese and salt and pepper to taste, whisking until cheese is melted. Peel potatoes and slice about 1/8 inch thick (3mm or 4mm slicing disk). In prepared baking dish make 5 layers each of potatoes and sauce, beginning with potatoes and ending with sauce. Scalloped potatoes may be prepared up to this point 2 hours ahead and kept covered. Sprinkle bread crumbs on top and bake, uncovered, in oven 1 hour, or until potatoes are tender and top is golden. Ratio: About 3/4 cup shredded cheese to 1 pound of potatoes