Cook elbow noodles as directed on package.
Meanwhile, in a large saucepan, melt butter. Stir in flour until smooth. Gradually add milk and stir until all lumps have dissolved. Bring to a boil; cook and stir for 2 minutes. Reduce heat; stir in cheeses, salt, and pepper until cheeses have melted and sauce is smooth.
Drain macaroni and add to sauce and mix well. Stir in chopped pepperoni. Transfer to a greased 3-quart baking dish.
Bake, uncovered, at 350 degrees for 30 minutes or until bubbly. Remove from oven and sprinkle breadcrumbs over top. Return to oven for another 10 minutes.
