Filleting a flatfish is similar to filleting a roundfish, but there are just enough differences to warrant this step-by-step. Done right, you can leave a carcass with very little meat on it.First set up your work station. You should have plenty of room to maneuver, a stout cutting board, a fillet knife or a boning knife with a very flexible blade, a bowl for the fillets, a bowl for the carcass, and a cleaver -- although the cleaver is optional.
The cleaver and the carcass bowl are in case you plan on saving it to make stock with later. This is something I highly recommend, as the bones and heads of all flatfish make superior stock.