To begin this recipe you need to set to work preparing the salsa verde ingredients and have them lined up ready. Now crush the garlic with the salt using a pestle and mortar and, when it becomes a purée, simply add all the prepared ingredients and whisk well to blend them thoroughly.
Now turn the oven on at gas mark 6, 400°F (200°C). Next prepare the potatoes: put the kettle on, then peel and chop the potatoes into 1/4 inch (5 mm) slices. Place them in a shallow saucepan, then add salt and just enough boiling water to barely cover them. Simmer, with a lid, for 7-8 minutes – they need to be almost cooked but not quite – then drain off the water and cover them with a cloth for 2-3 minutes to absorb the steam.
Now arrange half the potatoes over the base of the baking dish and season well, wipe the fish with kitchen paper, cut it into 11/2 inch (4 cm) chunks and arrange it over the potatoes, seasoning again. Next spoon the salsa verde all over and arrange the rest of the potato slices over, overlapping them slightly. Then brush them lightly with the olive oil, season once more and sprinkle the cheese over. Now bake the whole lot on a high shelf of the oven for about 30 minutes, by which time the fish will be cooked and the potatoes golden brown.
