Heat oven to 350 F.
Lightly butter a 2 1/2-quart baking dish.
Cook macaroni in boiling salted water following the package directions. Drain the pasta thoroughly and set aside.
In a large saucepan over medium-low heat, melt butter; add flour and stir until blended. Stir in salt, pepper, and mustard. Gradually stir in the milk and continue cooking, stirring, until mixture is thickened. Stir in cheeses until melted and smooth. Add the macaroni and stir to blend.
Spoon the macaroni and cheese mixture into the prepared baking dish.
Combine breadcrumbs and melted butter, tossing to coat well; sprinkle over the macaroni mixture. Lightly sprinkle with paprika.
Bake for 25 minutes, or until browned and bubbly.