Preheat oven to 400° F. Melt 1 tablespoon butter and combine with breadcrumbs and Parmesan cheese in a small bowl. Set aside.

Cook pasta per package directions, drain, and return to pot.

In large heavy saucepan, melt remaining butter over low to medium heat. Add flour and whisk until golden. Add milk; continue whisking and cooking until sauce thickens slightly. Add dry mustard and grated cheese, whisking until cheese melts into sauce. Taste and add salt and pepper as desired.

Pour sauce over pasta and stir to combine well. Transfer macaroni to a 4-quart baking dish. Sprinkle with breadcrumb mixture.

Bake 25 to 30 minutes until lightly golden and bubbling.