Preheat the oven to 180°C/gas mark 4

For the lentils, heat the oil and butter in a frying pan over a low-medium heat. Add the onions and carrots and sweat for 15 minutes

Add the garlic, thyme, bay leaf, celery and pancetta. Sweat for 5 minutes, then drain to remove any excess fat

Line a large bowl with a piece of muslin cloth and pour all of the cooked ingredients into the bowl. Tie the muslin loosely to encase the ingredients before adding to a large pan. Add the lentils, cover with water then bring to the boil. Turn the heat down and leave to simmer for 30 minutes

Once the lentils are cooked, season with salt and pepper and leave to cool. Once cool enough to handle, squeeze the muslin bag over a bowl to catch all of the juices. Discard the muslin and vegetables and reserve the juices

Place a frying pan over a high heat and add oil. Once hot, add the pancetta and fry for 1-2 minutes, then pour in the sherry vinegar to deglaze

Add the lentils and pre-boiled carrots to the pan with a splash of the reserved cooking juices. Finish with the butter, olive oil and spring onions and keep to one side while you cook the cod

Season the fillets of cod and place skin-side down onto a baking tray. Cook in the oven for 4-5 minutes until cooked through

Remove the fish from the oven, carefully flip the cod over and leave to rest for a few minutes. Drizzle with olive oil and then serve onto plates with the lentils