Preheat the oven to 400º F. Sautée the chopped shallots with chopped chantrelles and sherry for about 5 minutes. Boil the potatoes for 10 minutes until they are starting to get soft. Slice the potatoes and place them on the bottom of a baking dish. Pour 1/3 of the mushroom mix onto the potatoes. Sprinkle 1/2 of the parsley over of the mushrooms, then lay the fish down on top. Sprinkle the rest of the parsley on top of the fish, then the remaining 2/3 of the mushrooms, with any remaining liquid. Place the sprigs of brocoli around the edges. Bake at 400º for about 10 minutes, until the fish begins to brown but is still juicy inside. Move the assembly over to a presentation dish and serve.