• 2 tablespoons extra-virgin olive oil, plus more for frying
• 3 celery ribs, very thinly sliced
• 1 medium onion, halved, very thinly sliced
• Salt
• Freshly ground black pepper
• ⅓ cup sherry vinegar
• 5 whole black peppercorns
• 5 whole coriander seeds
• 2 teaspoons finely chopped sage
• 2 teaspoons finely chopped tarragon
• 1½ pounds skinless perch or trout fillet, pin bones removed
• Unbleached all-purpose flour for dredging

Heat oil in heavy large skillet over medium heat. Add celery, onion and pinch salt and pepper. Reduce heat to medium-low and cook, stirring occasionally, until mixture is deep golden brown, about 40 minutes.

Add vinegar, whole peppercorn and coriander to celery mixture; cook 1 to 2 minutes to warm mixture through. Remove from heat, stir in sage and tarragon and cover to keep warm.

Cut fish into pieces, about 1½ inches wide. Dredge pieces in flour, shaking off excess.

Heat enough oil to come ½ inch up sides of pan in heavy medium skillet over medium-high heat, until hot but not smoking. Working in batches, fry fish until cooked through and golden on all sides, about 1 minute per side; transfer to paper towels to drain. Season with salt and pepper.

Transfer vinegar mixture to a platter, top with fish and serve warm or at room temperature.