Mix the softened butter with the dill, garlic, lime zest and juice, salt and pepper and set aside. This can be made a few days in advance and kept in the fridge.
In a frying pan, heat 1 tbsp of vegetable oil over a medium heat. Once the oil is up to temperature, place the cod skin side down and cook for 6-8 minutes or until the skin has gone crisp. Turn the fish over and cook for 3 minutes. Add the lime butter to the pan, then remove from the heat.
Once the butter has melted, lift the fish onto serving plates and generously spoon over the melted butter from the pan.
Serve with roast potatoes, wilted spinach and a sprig of dill.