Lay the fish on a flat work surface and hold it by the tail with one hand. Gripping a knife with your other hand, scrape the scales off the fish starting working from the tail towards the head. Once the fish is perfectly descaled, rinse it under cold running water.
Using a sharp, pointed knife, make an incision perpendiculr to the gill.
Insert your index finger in the hole and try to open it entirely. Then wash the fish under cold running water, both inside and out.
Make an incision in the skin near the head of the fish and remove the skin by pulling forefully. Pull from the head towards the tail.
Repeat on the other side.
Fillet the sole by cutting around the bones. Now, insert your knife in the flesh of the fish, just behind the head and above the spinal bone. Carefully move your knife back and forth in a sawing motion, moving it along the spine down towards the tail.. Turn the fish and repeat. Then flip the fish and remove the other two fillets.
Filleted sole can be cooked in various ways: cooked in a pan, flattened to form a terrine, used to stuff other fish.