2 (16 ounce) packages elbow macaroni

1/2 cup butter

1/2 cup all-purpose flour

1/2 teaspoon dried thyme

1/2 teaspoon cayenne pepper

1/4 teaspoon white pepper

6 cups milk

2 pinches ground nutmeg

1/2 teaspoon Worcestershire sauce

2 teaspoons salt

6 cups shredded sharp Cheddar cheese, divided

2 teaspoons Dijon mustard

1 cup panko bread crumbs

2 tablespoons butter, melted