It can be very rewarding to buy your fish, take it home, then prepare it yourself. The majority of home and professional chefs are taught to fillet flat fish such as Turbot, Sole and Plaice into quarters. This is the easiest and quickest way to produce fillets, however, it will only ever yield quarter fillets. On many occasions the whole fillet, which does look more impressive, is needed for certain dishes especially those that require rolled finishes. I used whole plaice when self teaching myself to fillet flatfish and would suggest this species as a great option as it is generally the cheapest available. The example below is with a lemon sole which is as easy to fillet as a plaice. Personally i would say Dover Sole are the most difficult of the flats to work with as they have the softest of bones.
After removing the head place the fish white skin down on your chopping board. The topside of a flat fish is thicker than the underside and as they are not square by nature this means it will lay flatter on your board. Insert the point of your knife above the bone and gently insert.
With your spare thumb lift the fillet to expose the bone which will allow you to see where you are cutting and then continue to caress the knife all the way along the skeleton until the point appears by the tail.
Now the hard bit that isn't required if quarter filleting. Gently roll the point over the raised centre bone at either head or tail end, which ever you feel comfortable with, then run the knife from one end to the other.
Remove the knife, turn it in your hand so it will run flat to the bone, then in one sweep run your blade over the skeleton.
So we have a Lemon Sole with the top side fillet removed. You can now see the ridge that runs down the centre.
The fish is then turned over and the same process is followed on the B-side. Do take care as the underside is up to a third thinner so requires a little more care when rolling over the centre ridge.
So there you have two clean fillets of Lemon Sole. These can be trimmed tighter to the flesh and/or skinned quite easily with a flexible blade. This fish had a little roe so the trimming was minimal.