Method

1. Roughly chop the cod and toss in lime juice and leave to marinate for 15 minutes. The acid in the lime will slightly 'cook' the cod - you can see the flesh become slightly transparent.
2. In the meantime, cook the Marshalls macaroni according to pack instructions. Add the chopped sweet potato to the water as well and cook till potato is just firm to tough.
3. Make a cheese sauce, by melting butter, add flour, then milk and stir in grated cheddar cheese, leaving a tablespoon aside for the topping.
4. Add the cod to the cheese sauce and cook for 5 minutes, then add the drained macaroni and sweet potato and stir well, then cook together for a further 5 minutes and transfer to a flameproof dish.
5. Sprinkle with cheese and cook under a preheated grill until golden.