Baked Flounder with Roasted Tomatoes

"Here Dijon mustard serves a dual purpose: It flavors the delicate fish, and helps the breadcrumb coating stay in place as the fish cooks. Tilapia can be used in place of the flounder."

Make 4 servings.

Ingredients :

• 6 plum tomatoes, halved lengthwise
• 2 tablespoons olive oil, plus more for one of the baking sheets
• 3/4 teaspoon dried tarragon
• Pinch sugar
• Coarse salt and ground pepper
• 1/3 cup mayonnaise
• 1 tablespoon fresh lemon juice
• 3 slices white sandwich bread (about 1 ounce each), torn into large pieces
• 4 flounder fillets (1 1/2 pounds total)
• 2 tablespoons Dijon mustard

Directions :

1. Preheat oven to 450, with racks in upper and lower thirds. Place tomatoes on a rimmed baking sheet. Sprinkle with 1 tablespoon oil, teaspoon tarragon, sugar, salt, and pepper; toss to coat. Arrange tomatoes cut side up. Roast on lower rack until tender, 20 to 25 minutes. (Keep oven on for fish.)
2. Meanwhile, make sauce: In a small bowl, whisk together mayonnaise, remaining 1/2 teaspoon tarragon, and lemon juice; season with salt and pepper. Set aside.
3. Line a rimmed baking sheet with aluminum foil and brush with oil. In a food processor, place bread, a pinch each salt and pepper, and remaining tablespoon oil; pulse until fine crumbs form.
4. Lay fillets flat on prepared baking sheet; season with salt and pepper. Spread top sides with mustard; sprinkle with bread crumbs, pressing to adhere. Bake on upper rack until fish is cooked through and crumbs are browned, 6 to 8 minutes. Serve with tomatoes and sauce.