- 2 tablespoons golden raisins
- 1/2 cup white balsamic vinegar, or 1/2 cup cider vinegar mixed with 2 tablespoons sugar
- 1 medium red onion, thinly sliced crosswise
- 2 1/2 tablespoons olive oil
- 1 (1-pound) piece halibut fillet with skin (about 1 1/2 inches thick) or 2 (8-ounce) red snapper fillets with skin
- 2 tablespoons potato starch
- 1 large fennel bulb (sometimes called anise) with fronds
- 2 1/2 ounce radish sprouts or watercress sprigs, trimmed (2 cups)
- 2 tablespoons white balsamic vinegar, or 2 tablespoons cider vinegar mixed with 1 1/2 teaspoons sugar
- 1/4 cup olive oil
- 1/4 teaspoon sugar
- Simmer raisins in vinegar in a small saucepan until raisins are plump, 3 to 5 minutes, then cool.
- Cook onion in 1 tablespoon oil in a 12-inch nonstick skillet over moderate heat, stirring occasionally, until softened, 4 to 6 minutes. Remove skillet from heat and transfer half of onion to a 9-inch square glass or ceramic baking dish with a slotted spoon, spreading evenly. Reserve remaining onion.
- Cut fish into 6 equal pieces. Pat dry and season with salt and pepper. Spread potato starch on a plate and dredge fish in it, shaking off excess.
- Heat remaining 1 1/2 tablespoons oil in skillet over moderately high heat until hot but not smoking, then sauté fish, skin sides down, until lightly browned, 1 1/2 to 3 minutes. Turn fish over and sauté until lightly browned and just cooked through, 1 1/2 to 3 minutes more.
- Arrange fish on top of onion in baking dish, then top with reserved onion and drizzle with raisins and vinegar. Cool completely, then marinate, covered and chilled, at least 8 hours. Bring to room temperature.
- Tear enough fennel fronds to measure 1 tablespoon. Trim stalks flush with bulb and discard stalks. Quarter bulb lengthwise, then cut lengthwise into paper-thin slices with a mandoline or other manual slicer. Transfer slices to a bowl and toss with radish sprouts.
- Whisk together vinegar and oil, then whisk in sugar and salt and pepper to taste. Toss vegetables with half of dressing and divide among 6 plates.
- Remove onion from top of fish, reserving it, and put a piece of fish on top of each salad. Mound all of onion and raisins on top of fish, then drizzle with remaining dressing and sprinkle with fennel fronds.