Heat broiler. In a medium saucepan, melt 3 tablespoons of the butter over medium-high heat. Add carrot, celery, onion and potato. Saute 5 minutes, until onion is softened.
Stir in flour. Pour in clam juice, cream, wine, salt and pepper. Bring to a simmer. Simmer 13 to 15 minutes, until vegetables are just tender. Stir in scallops and shrimp. Cook 4 minutes, stirring occasionally until seafood is cooked through.
Meanwhile, combine bread, basil and a pinch of salt in a food processor. Pulse until bread crumbs are formed. Melt remaining 2 tablespoons butter, and toss with bread crumbs until moist.
Divide seafood mixture between four 12-ounce ovenproof dishes. Top with bread crumbs; broil 2 minutes until browned. Makes 4 individual casseroles.