Butter a 4 quart baking dish.
Preheat oven to 375 F.
Bring a large pot of water to boil and cook the pasta until al dente.
Drain well and pour into greased baking dish.
Meanwhile, in a medium saucepan over medium heat, melt the butter.
Stir in the dry mustard and flour and simmer for 2 minutes being careful to prevent butter from burning.
Still over medium heat, add the milk and bring to a low boil.
Stir in the cheese cubes, reduce the heat and continue stirring until cheese is all melted.
Pour evenly over the macaroni.
Sprinkle top with Panko (½-1 cup's worth) and then paprika.
Bake for 25-35 minutes or until starting to bubble in center and nicely browned.