Preheat oven to 400 degrees.
Cook pasta according to package directions.
Meanwhile prepare the cheese sauce. Melt the butter in a sauce pan over medium heat. Whisk in the flour, dry mustard, a pinch of salt and pepper to taste. Cook for 1 minute.
Whisk in the milk and half and half. Bring to a gentle boil, reduce heat and simmer until thick.
Turn off heat and add the cheese using figure-eight strokes.
Add pasta to cheese sauce and stir to combine.
In a large casserole or individual baking dishes add mac ‘n cheese. Top with brisket, barbecue sauce, extra cheese, and French fried onions.
Bake for 6-8 minutes until the cheese is melted and the French fried onions begin to brown.
