1

Work under cold running water or over several sheets of newspaper. Grip the fish by its tail and scrape it from the tail toward the head, working against the direction in which the scales lie, using a fish scaler or the blade of a blunt, thick-bladed knife.

2

Cut away the dorsal, pelvic, and anal fins using a strong pair of kitchen scissors.

3

Slit open the belly of the fish from the anal fin up to the head and pull out the guts.

4

Preheat the broiler. Slash the skin of the mackerel at 1/2-inch (1-cm) intervals on both sides, from the head all the way down to the tail, taking care not to cut too deeply into the flesh.

5

Season the fish inside and out with a little salt and pepper. Wash the seaweed and spread it over the bottom of a saute pan large enough to hold the fish in a single layer (if you don't have a pan large enough, use two). Add 1 1/4 cups (300 ml) of water, put the fish on top, and cover with a tight-fitting lid. Set to one side.

6

For the sauce, melt 2 tablespoons (25 g) of the butter in a pan. Add the fennel, onion, and garlic, and cook for 5 minutes until soft but not browned. Add the stock, white wine, and some salt and pepper, and simmer for 15 minutes until the vegetables are very soft and most of the liquid has evaporated.

7

Spoon the mixture into a blender and let cool slightly. Then add the Pernod, lemon juice, and egg yolks. Melt the rest of the butter in a clean pan. As soon as it begins to bubble, turn on the blender and blend the contents for 1 minute. Then slowly pour in the hot melted butter to make a hollandaiselike mixture. Pour the sauce into a bowl and stir in the chopped herb fennel and some seasoning to taste. Keep warm.

8

Place the pan of fish and seaweed over a high heat. As soon as some steam starts to leak from underneath the lid, turn the heat down and steam for 5 minutes until the fish are cooked through. Without lifting the lid, take the pan of fish to the table, together with the fennel butter sauce. Remove the lid so your guests can appreciate the aroma and serve with some plain boiled potatoes.