Ingredients
1/8 teaspoon saffron threads
Kosher salt and freshly ground pepper
2 tablespoons hot water
3 tablespoons extra-virgin olive oil, divided, plus more for drizzling
2 tablespoons unsalted butter, divided
2 pounds small leeks, white and light-green parts only, cut on the bias into 2-inch pieces (5 cups) and thoroughly washed and drained
1/4 cup dry vermouth or dry white wine
1 cup halved cherry or grape tomatoes
1 1/3 cups reduced-sodium chicken broth
1 1/4 pounds skinless meaty white fish, such as halibut, cut into 4 pieces (each about 5 ounces and 1 inch thick)
1 teaspoon grated lemon zest
1/3 cup mixed fresh tender herbs, such as snipped chives, chervil, and tarragon
Flaky sea salt, for serving (optional)
Preparation
Crush saffron and a pinch of kosher salt with a mortar and pestle (or with the side of a large knife) until combined. Stir in hot water; set aside.
Heat 2 tablespoons oil and 1 tablespoon butter in a large straight-sided skillet or braiser pan over medium. Add leeks; season with kosher salt and pepper. Cook, stirring occasionally, until bright green and evenly coated, 3 to 4 minutes. Add vermouth and tomatoes; cook 1 minute.
Add saffron water and broth; bring to a boil, then reduce heat to medium low and simmer, partially covered, until leeks are completely tender, about 25 minutes.
Season both sides of fish with kosher salt and lemon zest; drizzle with remaining 1 tablespoon oil. Nestle into leek mixture, cover, and cook until fish is opaque and just cooked through, 5 to 6 minutes. Stir remaining 1 tablespoon butter into broth. To serve, toss together herbs and sprinkle over fish, then drizzle with more oil and season with flaky salt.
