Whilst the barbecue is heating up you should be preparing the onion butter.

To do this into a small frying pan (skillet) place the better and once it is melted to it add the finely chopped onion and allow it to cook for about 1 to 2 minutes.

Then to this you add the wine and leave to simmer for 3 minutes.

When this time has elapsed remove from the heat and let it cool slightly.

As soon as the barbecue has reached the right temperature you should now lightly brush the cod fillets with the olive oil and sprinkle on some salt and black pepper before then placing on to the lightly oiled barbecue grill.

Cook the fish on one side for about 8 minutes before then turning it over and basting with some of the butter sauce you made earlier.

Now allow the fish to cook for a further 6 to 7 minutes or until you notice the flesh has begun to turn opaque.

During this cooking time it is important that you baste the fish with the butter sauce a further 2 or 3 times before then removing from the heat and placing on a clean plate and serving with the wedges of lemon.