For a bit of inspiration, here’s a gourmet recipe made with Cromaris sea bream, created by Michelin-starred Italian chef Giorgio Locatelli.
Pop the basil leaves into a food processor and blitz until finely chopped. Add the butter and blend again until you get a smooth, pale-green, creamy mixture. Scrape it into a bowl and chill in the fridge until you need it.
Put the whole potatoes (skins on) into a pot of cold, salted water. Bring to the boil, then turn the heat down and simmer until they’re nice and tender (around 1 hour, depending on their size). When the potatoes are nearly done, gently warm the milk in a small saucepan - you don’t want it to boil. Peel the potatoes, let them cool slightly, then mash until smooth. Stir in the warm milk, season to taste, and keep the mash somewhere warm.
Meanwhile, heat up two non-stick frying pans and split the sunflower (or vegetable) oil between them. Season the fish fillets and lay them in the pans skin-side down. Give them a gentle press so the skin sits flat, then cook until the skin is golden and crisp and the flesh has turned white and opaque. Flip the fillets over and turn off the heat.
Cut the basil butter into cubes. Put the mash back over a low heat, add the basil butter cubes and stir until it’s melted through and glossy. Spoon some mash into the middle of each plate, place the fish on top, drizzle a little olive oil over each fillet, and serve.