-
1
Preheat oven to 375F.
-
2
Spread 1 1/2 bunches of dill evenly in baking pan, reserving remainder for garnish.
-
3
Simmer water, clam juice, onion, salt, peppercorns, and bay leaf in a 2- to 3-quart saucepan, uncovered, 10 minutes, then pour hot mixture over dill in pan.
-
4
Arrange fish, skin sides up, in 1 layer on dill in pan and season with salt and pepper.
-
5
Bake, uncovered, in middle of oven until fish is just cooked through, 10 to 20 minutes, depending on thickness of fillets.
-
6
Transfer fish, skin sides up, to a platter and keep warm, loosely covered with foil.
-
7
Pour cooking liquid through a sieve into a bowl, pressing hard on solids.
-
8
Discard solids and reserve 2/3 cup cooking liquid.
-
9
Whisk together egg yolk and lemon juice in a small bowl.
-
10
Beat egg white with a clean whisk in a medium bowl until it just holds stiff peaks, then whisk in yolk mixture.
-
11
Pour egg mixture into a 2-quart heavy saucepan, then whisk in reserved cooking liquid.
-
12
Cook sauce over moderately low heat, stirring constantly with a wooden spoon (it will be foamy), until it is thick enough to coat back of spoon and registers 170 to 175F on an instant-read thermometer, 2 to 3 minutes.
-
13
(Do not let boil.)
-
14
Immediately pour sauce through a fine sieve into a bowl, then serve over fish.
