Hake stuffed with langoustines

1 hake of 2 1/2 kgs
500 g. langoustines (or big prawns), cooked and shelled
250 grs. prawns
4 onions
2 eggs
2 tablespoon fresh breadcrumbs
2 glasses Manzanilla
100 g. Gruyere cheesse
150 grs. mushrooms
100 g. butter
salt and ground pepper

1. Pound the fish with a wooden pestle and remove the spine.
2. Peel and chop the onions and wipe and reserve the mushrooms.
3. Spread three of the chopped onions on the bottom of an oven dish large enough to hold the fish.
4. Heat half of the butter in a frying pan and fry the rest of the chopped onions.
5. Stir them with the langoustines, the prawns, salt, pepper, mushrooms and a glass of Manzanilla.
6. Add the beaten eggs, and breadcrumbsand stir well to obtain a smooth filling. Check the Sherry, sal and pepper, and reserve.
7. Open the fish like a book and fill it with this mixture, adding the grated cheese. Fold back the flap and pat it into shape with the hands covered in flour so that the filling does not scape.
8. Put the fish and the layer of chopped onions in the oven dish, season with salt and pepper, add a glass of Manzanilla and a little stock and dot with butter.
9. Bake in the oven for approximately 30/35 minutes. It is is very thick it may require to stay a little longer in the oven; should this be the case cover it with kitchen foil so that it does not dry out.
10. If served hot, it may be accompanied by bechamel or mornay sauce.
11. If served cold, it may be accompanied by cocktail or mayonnaise sauce. In this case the skin should be removed while it is lukewarm.
12. Transfer the fish to a serving dish and decorate with asparagous tips, peas, beatrrot and julianned carrot and lettuce.