Cod tongues are a real delicacy. In Spain salted tongues are twice as expensive as the finest dried cod
Mix together the mayonnaise, tomato ketchup, tomato purée, onions, dill and roe in a bowl and stir until everything is well mixed.
Place the cod tongues in a steamer with a small amount of water. Steam the tongues for seven minutes. Drain on baking paper.
Mix together the flour, mustard power and salt. Turn the fillets and tongues in the mixture.
Heat the oil to around 170oC. Fry the fish until it is golden brown. Add salt to taste and serve immediately.