1

With the back of the fish facing you, make a cut behind the back of the head, down to the backbone, using a sharp, thin-bladed, flexible knife.

2

With the knife still in place, turn it toward the tail and start to cut away the fillet. As soon as the whole blade of the knife is underneath the fillet, put your other hand flat on top of the fish and cut it away in one clean sweep, keeping the knife as close to the bones and as flat as possible.

3

Lift off the fillet, then turn the fish over and repeat the princess.

4

First make the sauce: Put the sherry vinegar and shallot in a small pan and bring to a boil. Boil until reduced to about 1 teaspoon. Half-fill a pan with water and bring to a boil, then reduce to a simmer and rest a glass or stainless-steel bowl on top. Put the water, egg yolks, and sherry vinegar reduction into the bowl and whisk vigorously until voluminous and fluffy.

5

Remove the bowl from the heat and gradually whisk in the clarified butter, building up an emulsion as if making mayonnaise. Add the lemon juice, cayenne pepper, chopped mint, 1/2 teaspoon of salt, and some black pepper. Set aside and keep warm in a bowl of warm water.

6

Bring 5 cups (1.2 liters) of water and 2 tablespoons of salt to a boil in a large, clean frying pan. Reduce to a simmer, then add the mackerel fillets and poach for 3 minutes, turning them over halfway through cooking. Lift out, draining away the excess water, and put two mackerel fillets on each warmed plate. Spoon a little of the sauce over the fish and the rest around, and garnish with sprigs of fresh mint.