A gutted, scaled whole fish, with its head, is ideal for salt-crusting, but a headless fish works, too. In this recipe, the salmon is rich and flavorful with a silky texture, so the tangy, crunchy relish makes for a delicious contrast.
1 whole 2-1/2 to 3 lb. salmon
Optional aromatics for the cavity: fennel fronds, thin slices of shallots, thin slices of lemon or orange
2 tsp. olive oil
6 cups kosher salt
4 large egg whites
1 recipe Fennel, Green Olive, and Mint Relish
Position a rack in the center of the oven and heat the oven to 400°F.
Apply the salt crust
Rinse the salmon well, inside and out. Make sure there are no loose scales on the skin. Pat the salmon completely dry with paper towels and put it on a large rimmed baking sheet or cutting board.
Stuff the cavity of the salmon with your choice of aromatics, if using. Rub the skin of the fish all over with the olive oil (this will make it easier to remove the salt crust after roasting).
In a large bowl with a rubber spatula, mix the salt with the egg whites and 1/2 cup water. Spread enough of the salt mixture on the bottom of a large rimmed baking sheet to make a bed about 1/4 inch thick and roughly the same size as the salmon. Put the fish on top of the salt bed. Using your hands, coat the fish with the remaining salt mixture to make a 1/4-inch-thick crust, molding it around the contours of the fish. (the tail or head may extend beyond the rim of the pan and therefore won’t be covered with the salt mixture—this is fine.)
Roast the Salmon
If using a remote probe thermometer, insert the probe near the spine behind the head (the thickest part of the fish). If using an instant-read thermometer, apply a marker (such as a piece of garlic or shallot) to the crust at this spot so you know where to check the temperature later.
Roast until the thermometer registers between 135°F and 140°F, about 35 to 45 minutes (start checking at 35 minutes). Let the fish rest in its crust for 5 to 10 minutes before serving.
Serve the fish
Tap the salt crust with the back of a large metal spoon to break it.
Using a large fork and the spoon, push the crust to the side so the fish is exposed. Then use a pastry brush to flick away any salt that’s sticking to the skin.
With the spoon, gently scrape the skin off the top of the fillet and push it to the side.
Run the spoon along the spine to separate the flesh from the bones. Use the fork to help move the flesh to serving plates.
Once you’ve removed all of the top fillet, grip the tail end of the bones and pull them away to expose the bottom fillet. Push aside any aromatics stuffed into the cavity. Use the spoon to separate the bottom fillet from the skin.
Spoon some of the fennel relish onto each portion and serve.
