Remove (or get your fishmonger to remove) the skin from the cod fillet. Use a big knife to chop the cod
Picture and put into a bowl. Beat the egg in a small bowl. Chop the tarragon to yield a good handful, add to the cod along with the juice from half a lemon, about half the beaten egg, and a tablespoonful of flour Stir in well using a fork with a teaspoonful of salt and good grind of fresh black pepper. Put to one side for a bit.