Perfect Poached Fish Fillets with Crispy Scallions and Miso-Ginger Vinaigrette
Thick white fish fillets with a meaty texture, like halibut, cod, haddock, bass, or snapper, work best in this recipe. Do not use extra virgin olive oil or the sauce will be bitter. Because most fish fillets differ in thickness, some pieces may finish cooking before others—be sure to immediately remove any fillet that reaches 130 to 135 degrees. The half onion in step 2 is used to displace the oil, however, a 4-ounce porcelain ramekin may be used instead.
4 skinless white fish fillets, 1 inch thick (about 6 ounces each)
3/4 cup olive oil (see note)
1 bunch scallions, whites cut into 1/4-inch rings, greens reserved for vinaigrette and garnish
2 teaspoons cornstarch
½ onion, peeled (see note)
6 scallion greens
4 teaspoons white miso
2 tablespoons mirin
2 tablespoons lime juice
2 teaspoons coarsely chopped ginger
1/2 teaspoon sugar
1. For the Fish: Adjust oven rack to middle position and heat oven to 250 degrees. Pat fish dry with paper towels and season with 1 teaspoon salt (1/4 teaspoon per fillet) and set aside. Combine scallion whites and cornstarch in small bowl and toss to coat. Heat 1/4 cup of oil in 10-inch nonstick skillet over medium heat until shimmering. Add scallion whites to skillet and cook, shaking pan occasionally, until crisp and golden, 1 to 2 minutes. Pour contents of skillet through fine-mesh strainer into bowl or measuring cup; transfer scallions to paper towel-lined plate and season with salt. Do not wash strainer.
2. Rinse skillet thoroughly under cold water, and wipe dry with paper towels. Transfer strained oil to cooled skillet and add remaining 1/2 cup oil (combined oil should register about 100 degrees). Place onion half in center of pan and arrange fish fillets, skinned-side up, around it (oil should come roughly halfway up fillets). Spoon oil over each fillet, cover skillet, transfer to oven, and bake for 18 minutes.
3. Remove skillet from oven and, using spatula, carefully flip fillets. Cover skillet, return to oven and continue to bake until fish registers 130 to 135 degrees, 10 to 18 minutes longer. Gently transfer fish to serving platter and tent loosely with foil.
4. For the Vinaigrette: Combine all ingredients in blender. With blender running on medium speed, slowly drizzle in 1/2 cup fish cooking oil. Blend on high speed until sauce is smooth, about 1 minute. Add any accumulated fish juice from platter, season with salt to taste, and blend for 10 seconds longer. Strain sauce through fine-mesh strainer, pressing on solids to extract as much liquid as possible (discard solids).
5. To serve, pour sauce around fish. Garnish each fillet with reserved crisped scallion whites, scallion greens, and radish (if so desired). Serve immediately.