Preheat oven to 350 degrees F (175 degrees C). Combine the mashed sweet potatoes with the white sugar, soft butter or margarine, beaten eggs, vanilla and milk. Spoon into a 2 quart oven proof baking dish. Combine the coconut, flour, brown sugar, chopped nuts and melted butter. Sprinkle over the top of the sweet potatoes. Bake at 350 degrees F (175 degrees C) for 30 to 35 minutes.