Season the beef generously with salt and pepper. Pour the oil into a Dutch oven set over a moderate-high heat and sear the beef on all sides until well-browned. Scatter with Creole seasoning and celery salt.
Return the beef then pour in the stock and barbecue sauce, then add water to cover. Bring to a simmer, fit the lid, then cook gently for 3 hours, until very tender. Remove the beef and set aside to cool slightly.
Slice the beef into 12 pieces, then dust with half the flour. Whisk the remaining flour with 2 cups water, dip the beef pieces, then fry in hot (180°C) vegetable oil for 3 minutes, until very crisp. Drain on kitchen paper then place the cheese slices on top while hot to melt.
Halve the rolls and arrange the lettuce on the bases, then top with the beef, mustard and smokey barbecue sauce.