01 - Boil elbow macaroni in a pot of salted water until just al dente. Drain well and set aside.
02 - Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1 minute. Gradually add milk, whisking constantly, until smooth. Simmer, stirring, until thickened. Stir in cheddar cheese, mustard if using, salt, and pepper until fully combined.
03 - In a large mixing bowl, toss together the cooked macaroni, pulled pork, barbecue sauce, and cheese sauce until evenly coated. Transfer the mixture to a greased baking dish.
04 - Distribute extra cheddar cheese and breadcrumbs over the surface for a crisp finish.
05 - Bake in a preheated oven at 375°F for 20 to 25 minutes, until the top is golden and the edges are bubbling.