1pound 12 ounces (860g) white fish fillet such as codlingcod, flounder, tilapia,
1cup (250 ml)crème fraîche or heavynon ultra-pasteurized heavy cream
2large egg yolks
pounds (750g)One and a half mussels or clams
1cup (250ml)dry white wine or brut cidersuch as Sauvignon Blanc
Several branches fresh flat-leaf parsley
2tablespoons (30 g)unsalted butter
The white part of 2 large leekscleaned, trimmed, sliced into thin rounds
1fennel bulbtrimmed and diced
1quart ( 1 liter)fish stocksee recipe,
1inbouquet garni (parsley stemsfresh thyme branches, dried bay leaves, wrappedgreen leek leaf and tied together with kitchen string)
9ounces (270 g)fresh sea scallopswith coral if possible or baby squid,
For the garnish:
1/2 cup( 5g)flat leaf parsley leaves
Zest from one-halflemoncut in very thin (julienne) strips
Cut the fish fillet into 2 x 1-inch (5 x 2.5cm) pieces and refrigerate until ready to use. Whisk together the crème fraiche and the egg yolks in a small bowl, cover, and reserve.
Remove the beards from the mussels, rinse them well, and transfer them to a large saucepan or stockpot. Add the wine, half of the diced onions and the parsley, cover, and bring to a boil over medium-high heat. Cook the mussels just until they open wide, shaking the pan regularly so they cook evenly. When the mussels are cooked, remove them from the heat. Transfer the mussels to a large bowl. Strain and reserve the cooking liquid - there should be about 2 cups (500 ml). If there is not quite 2 cups, simply add water to make up the difference. When the mussels are cool enough to handle, remove them from the shell. Reserve the meats and discard the shells.
Melt the butter in a large saucepan over medium heat and add the remaining onions, the leeks, and the fennel. Stir and cook until the onions and fennel are translucent and the leeks are beginning to turn tender, about 5 minutes.
Add the fish stock, the mussel cooking liquid and the bouquet garni to the pan. Increase the heat underneath the pan to bring the liquid to a simmer. Cook until the vegetables are tender through and the liquid has reduced by about one third, 20 to 25 minutes. Add the fish and push it gently down into the liquid, then add the scallops. If necessary to keep the liquid at a simmer, increase the heat under the pan and cook until the seafood is nearly but not quite cooked through, 4 to 5 minutes. Transfer the fish and the scallops to a warm bowl. Remove the bouquet garni from the cooking liquid and discard.
Whisk about ½ cup (125 ml) of the hot seafood cooking liquid into the egg yolks and cream mixture, then stir this mixture back into the seafood cooking liquid in the saucepan. Cook, stirring, until the soup thickens just slightly, being very careful not to let it boil. Return the fish and the scallops to the pan, first draining away any liquid they might have given up. Add the mussels to the soup and cook until all the seafood is hot through, about 5 minutes. Taste for seasoning.
Mince the parsley leaves and stir it, with the lemon zest, into the soup. Let cook an additional 2 to 3 minutes, then serve immediately into warmed, shallow bowls.