- Sprinkle swordfish steaks with J.O. Brand Blackened Seasoning on both sides. Preheat cast iron skillet until it smokes. Dip the steaks in the melted butter. Gently place swordfish in the skillet and cook for 2 minutes. Reduce heat and gently flip filets. Cook 10 min. total per inch of thickness. Pour 1 Tbsp. melted butter over each filet. Continue cooking until flaky and white.