Defrost frozen shrimps. Peel, wash and cut the potatoes into large pieces. Cover and cook in salted water for about 20 minutes.
In the meantime peel the shrimps, except for the tail fin. Wash the prawns and pat them dry. Rinse shrimp shells cold and drain. Clean and wash the celery. Peel onions and chop both finely.
Heat 1 tablespoon of butter. Roast the shrimp shells for approx. 3 minutes while turning. Add celery and half onions, cook for another 3 minutes. Dust with flour and sauté. Add wine, stock and cream, bring to the boil and simmer for about 5 minutes.
Season the sauce with salt, pepper and Noilly Prat. Pass through a very fine sieve and keep warm.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Grease four small refractory moulds. Drain the potatoes and mash them finely. Stir in mashed potatoes, parmesan, milk and egg yolk.
Pour potato mixture into the moulds. Bake in a hot oven for 10-15 minutes.
In the meantime, sort out the spinach, wash and drain. Heat 1 tablespoon of butter. Fry the rest of the onion until transparent. Add the spinach and cover and let it collapse. Season to taste with salt and nutmeg.
Keep warm as well.
Wash the fish and dab dry. Heat oil in a pan. Fry the fish for about 3-4 minutes on each side (be careful when turning, it falls apart easily). Season with salt and pepper. Remove and keep warm.
Fry the prawns in the hot frying fat for about 3 minutes, season as well. Arrange fish and prawns with spinach and sauce. Add mashed potatoes au gratin.