This dish is simple yet full of flavor because of the freshness of the fish. Grouper, striped bass, halibut, or salmon all make good substitutes, so buy what is in season.
Preheat oven to 400°.
Place tomatoes and leeks in a roasting pan; drizzle with 2 tablespoons olive oil, vinegar, rosemary, 1/4 teaspoon sea salt, and 1/4 teaspoon pepper. Toss gently to coat. Roast at 400° for 25 minutes, stirring leeks once halfway through cook time or until leeks are tender and tomato begins to shrivel.
Season fish fillets with 1 tablespoon olive oil, 1/2 teaspoon sea salt, and 1/4 teaspoon pepper. Melt butter with remaining 1 tablespoon olive oil in a large nonstick skillet over medium-high heat. Place fillets, skin side down, in pan; reduce heat to medium, and cook for 4 minutes, without moving fish. Carefully turn fillets over; and drizzle lemon juice over fish. Cook 2 to 3 minutes or until fish flakes easily with a fork, spooning pan liquid over fish while cooking. Remove fish from pan, and cover loosely to keep warm.
Add wine and broth to pan, and increase heat to medium-high. Reduce sauce to 1/4 cup (about 5 minutes) and until sauce is slightly thick and bubbly.
Place fillets on a platter or four individual plates, spooning sauce over and around fish; arrange leek and tomato mixture on each plate, and garnish, if desired. Serve immediately.