Rinse the Turbot under cold running water then pat dry with kitchen paper. Sprinkle a large baking tray with olive oil and place the fish into the tray. Using a sharp knife cut 2-3 times incisions into the thickest part of the top fillet. This will allow the fish to cook evenly.
Preheat the oven to 190ºC/ Fan 170ºC/Gas 5. Season the fish with salt and pepper. Sprinkle over shallots, sage, rosemary and butter. Add the wine and cook in the middle of the oven for 20-25 minutes.
Remove the fish from the oven and allow to rest for at least 5 minutes before serving. To serve remove portion sized pieces of the top fillets by sliding a palette knife under and lifting them off the bones. Once all the flesh is removed, lift the bones from the tail end to give access the two bottom fillets. Trap the lateral bones (which run all around the outside edge of the fish and into the fillets) with a knife and drag them away. Arrange the pieces onto preheated plates and sprinkle with the pan juices.
Serve with boiled, salted potatoes and brown butter sauce.