Macaroni and Cheese, not out of a box

Preheat the oven to 400 deg.  Cook 3 cups of dry elbow macaroni until aldente.  In a saucepan, melt 1/2 cup butter with 4 Tbl flour and make a roux, add 1 Tbsp of mustard, and pepper.  Once hot, slowly add 4 cups of milk and then slowly add 32 ounces of cheese (i used 16 ounces of velveeta and 16 ounces of shredded cheddar).  Cover the top with seasoned bread crumbs and then bake until bubbly and browned.