- In a large Dutch oven or other large pot, pour oil to a depth of four inches and heat over medium heat until it reads 375º on a candy or deep-fry thermometer (or use a countertop deep fryer).
- Pour the molasses mustard into a shallow dish or aluminum pan.
- In another shallow dish, stir together cornmeal, flour, barbecue rub, and salt.
- Coat each fish fillet in the mustard, then dredge in cornmeal mixture.
- Fry fillets in batches in hot oil until golden brown and cooked through, about 6 to 8 minutes per batch.
- Transfer to a paper-towel-lined plate to drain.
- Serve hot with more molasses mustard, Creole tartar sauce, jalapeño relish, or over roasted vegetables or cole slaw.