Preheat oven to 180ºC . Melt three tablespoons butter in a saucepan over medium heat. Cook scallions, stirring constantly about 10 minutes. Stir in curry powder, flour and salt, mixing well. Add milk, increase heat and cook until mixture boils and thickens. Remove from heat. Stir in sour cream, pasta and seafood, and pour mixture into a buttered baking dish.
Melt remaining tablespoon of butter and combine with bread crumbs. Sprinkle crumbs over seafood mixture and bake uncovered about 30 minutes.