4 pieces of skinless cod fillet or loin, about 200 g (7 oz) each
juice of 1 lemon
2 tablespoons olive oil
4 tablespoons chopped flat leaf parsley
4 slices of prosciutto
1 kg (2 lb) potatoes, peeled and cubed
50 g (2 oz) butter
4 tablespoons crème fraîche
100 g (3 1/2 oz) finely grated Gruyère cheese
40 g (1 1/2 oz) baby spinach leaves
salt and pepper
Place the cod, lemon juice, oil and parsley in a large non-metallic bowl and gently toss to lightly coat. Season with pepper. Tightly wrap each piece of fish with 1 slice of prosciutto and place on a large baking sheet. Place in a preheated oven, 220°C (425°F), Gas Mark 7, for 12–15 minutes, or until cooked through.
Meanwhile, make the mash. Cook the potatoes in a large saucepan of lightly salted boiling water for 15 minutes until tender. Drain, then return to the pan and mash with the butter and crème fraîche. Fold in the cheese and spinach until the cheese is melted and the spinach wilted, then season. Spoon on to 4 warm serving plates and top with the fish.