In a medium sized bowl toss the cubed bread with melted butter until evenly coated and set aside.

For the Macaroni and cheese:

Bring 4 quarts water to boil in a large pot, cook the pasta until tender, drain and set aside in a colander.

In a large saucepan, melt 5 tablespoons butter over medium heat. Add the flour, mustard, and cayenne and whisk until smooth {about 1 minute}. Slowly add in the milk, whisking constantly until the everything is well combined and there are no lumps.

Bring mixture to a boil, reduce heat to a simmer and continue to whisk until the sauce is nice and thick {about 3 minutes}.

Remove the saucepan from the heat and slowly stir in shredded cheese until fully melted. Fold in noodles.

Pour noodle mixture into a 9×13 casserole dish and cover with bread topping.

Turn the oven on to broil and toast the buttered bread until just browned. Serve warm.