Seafood Gratin

Name: Seafood Gratin
Prep time: 40 min
Cook time: 20 min
Total time: 1 h
Cuisine: French
Ingredients: 1 cup seafood stock or clam juice; 1 cup heavy cream; 1/2 cup plus 3 tablespoons good white wine, such as Chablis, divided; 3 tablespoons tomato puree; 1/2 teaspoon saffron threads; 8 ounces raw shrimp, peeled, deveined, and cut in half crosswise; 8 ounces raw halibut, cut into1-inch chunks; 8 ounces cooked lobster meat, cut into 1-inch chunks; 7 tablespoons unsalted butter, divided; 1 tablespoon all-purpose flour; Kosher salt; Freshly ground black pepper; 3 cups julienned leeks, white and light green parts (2 large); 1 1/2 cups julienned carrots (3 carrots); 1 cup panko (Japanese dried bread crumbs); 1/3 cup freshly grated Parmesan; 2 tablespoons minced fresh flat-leaf parsley; 1 tablespoon chopped fresh tarragon leaves; 1 tablespoon minced garlic (2 cloves)