Try serving this delightful seafood casserole in puff pastry cups with one of our many salads to impress everyone around the table.
Preheat oven to 400° F (200° C). Spray a 13-inch x 9-inch x 2-inch (33 cm x 22 cm x 5 cm) baking dish with non-stick cooking spray.
In a large non-stick pot, heat oil over medium heat. Add leeks and celery, stirring often, until leeks are softened. Stir in potato cubes, clam juice, Old Bay seasoning and pepper. Cover and bring mixture to boil, reduce heat and simmer until potatoes are tender, about 6 minutes.
In a small bowl, whisk milk, flour and mustard together. Add to potato mixture, stirring constantly.
Stir shrimp and fish into potato mixture and cook until the seafood is just cooked, about 2-4 minutes. Turn off heat and stir in crab, Gruyere cheese and dill. Transfer seafood mixture to the prepared baking dish.
Mix breadcrumbs with dill and Old Bay seasoning. Sprinkle topping over casserole. Bake casserole until bubbling and golden brown, about 25 minutes. Cool a bit before serving.