Preheat oven at 180° C.

• Clean the fish from the scales and the innards and carefully cut the two fillets. Season with salt and pepper and sauté them lightly into olive oil.
• Cut the potatoes into thin slices and sauté them lightly into olive oil until they soften.
• Thinly cut onion

1.  Lay the fish-fillets into an oven tray and the potatoes on the top of them. Cook for about 5-7 minutes and serve with the butter sauce.

2.  For the sauce, sauté the onion with  the butter (1 tablespoon) and pour the wine. Let the alcohol evaporate and then add the thinly cut rosemary and in small quantities the butter.

3.  Whip the sauce with a wire whisk until it sets, and then serve.