How to fillet a flat fish

This month with Leiths School of Food and Wine, we learn how to overcome the fiddly task of filleting a flat fish

Flat fish

All flat fish are classified as white fish, because the greatest concentration of their fat is contained in the liver, which ensures they have lean, white flesh. Although similar in appearance, each species has a distinctive flavour. They include plaice, lemon and Dover sole, brill, turbot, flounder and dabs. Skates and rays, with their cartilaginous (soft) frames, are also flat fish, although prepared differently as it is their wings that are prized in cooking.

This method removes four fillets from a flat fish. Fishmongers will often remove a whole side, so two double fillets from each flat fish. What is important is that you develop a method of filleting that you are comfortable with, that you use your knife safely and that you waste as little fish as possible. It is essential to use a very sharp knife, preferably with a long, flexible blade. First rinse the fish under cold water and dry with kitchen paper. Fish have a natural slime and rinsing it off makes it easier to handle.

Note: Now scrape the board to get rid of any loose bits of fish and rinse well under cold water, then wash well under hot water and detergent. Dry well.

1. Place the fish on a board, tail end towards you and darker side uppermost. Using a fish filleting knife, make an incision along the natural line running down the middle of the fish, from behind the head down to the tail

2. Make a small cut across the top of the tail

3. Make a cut from behind the head down to the edge of the fish behind the gill and head on both sides

4. Release a little of one of the fillets from the back bone, the full length of the fish. Then, using the flexibility and length of a fish filleting knife and long strokes, carefully release the fillet away from the skeleton. Try to keep the knife as flat against the bone as possible. You should hear a rasping sound as the knife blade works its way across the bones

5. As the knife approaches the edge, lift up the fillet to make it easier to see what you are doing

6. When you reach the frill, either grip the edge of the skin of the fillet and pull the fillet firmly away from the body, taking care not to damage the flesh, or cut the fillet away from the frill and main body of the fish

7. Repeat with the remaining top fillet. You need to ensure the knife blade is on the right side of the little vertical back bone before starting to remove the fillet

8. Turn the fish over and repeat the process on the pale underside. The skin here is a little tougher

Skinning a flat fish

If necessary, first wipe over the fillets with kitchen paper to ensure they are dry.

1. Place a fillet skin side down on the board with the narrow end towards you. There is a natural break between the fillet and the frill. Use the tip of a finger to identify and open this. Cut down this line to remove the frill on all 4 fillets. As you become more confident with your fish filleting and skinning skills, it may not be

necessary to remove the frill first; it will naturally come away as the fillet is skinned.

2. Take a little salt in the fingers of your non-knife hand and hold onto the end of the fillet tightly. Insert the knife between the skin and flesh, just in front of your fingers, at a 30–40° angle.

3. Now, holding firmly onto the skin, move the knife decisively to the left and right using an exaggerated sawing action, while maintaining a firm pressure with the knife on the fish skin, to start to release the flesh from the skin.

4. As you release more flesh adjust the position of the fingers holding the skin closer to the unreleased flesh. It is important to firmly press the knife blade against the skin, which is against the board. Work your way up the fillet like this, releasing the flesh as a whole fillet. Take care not to hold the knife blade too vertically or you will cut through the skin, but too flat against the skin and you will leave flesh on the skin; it takes some practice.

5. Repeat with the remaining 3 fillets. Wipe down the board with kitchen paper and lay the fillets on the board. Once skinned, trim the fillets as necessary, without wasting fish.

6. Feel the fillets all over for bones. Usually this method of filleting leaves the fillets bone free, but it is always good to check. Remove any small bones that you find with kitchen tweezers. The fillets are now ready to use.

Note When skinning, we find it easier to move the knife hand back and forwards, but, as with filleting, if you find it more comfortable to hold your knife hand steady and move the hand holding the skin from side to side, use this technique. You should adopt the method that feels the most comfortable and safest for you, and one that prevents wastage. It is easier to remove the darker skin from the fillets than the paler skin.

Presentation: Generally, when referring to fish, the non-skin side (the bone side) is the best looking side once cooked and will become the presentation side. The skin side generally has a little brown flesh under the skin which is evident after skinning. It also often has a ‘V’ pattern. You should cook the non-skin presentation side first, as this will almost always end up being the best looking and most appetising side.

When folding fillets, fold them skin side inwards, bone side outwards.

There are always exceptions. When grilling, you should grill the non-skin side last, as the second side of a grilled fillet is generally the better looking.

1. Finding the natural line between the fillet and the frill

2. Holding the narrow end of the fillet firmly and inserting the knife at an angle between the skin and the fillet

3. Working the fillet away from the skin, using a sawing action, while keeping the knife pressed firmly against the skin

4. Holding the skin closer to the unreleased flesh as you work towards the other end

5. Trimming the skinned fillets to neaten

6. The skinned fillets are now ready to cook

‘Leiths How to Cook by Leiths School of Food and Wine’ (Quadrille, £30) Photography © Peter Cassidy