Ingredients
4 x 125g/5oz salmon fillets, skin on
1 tbsp olive oil
For the watercress butter
85g/3oz watercress, finely chopped
75g/3oz unsalted butter, softened
1 shallot, finely chopped
1 tsp English mustard
freshly ground black pepper
For the watercress mash
675g/1½lb 'floury' or mashing potatoes, peeled and chopped into large chunks
salt and freshly ground black pepper
170g/6oz watercress, roughly chopped, plus extra to garnish
90ml/3fl oz fat-free yoghurt or milk
50g/2oz unsalted butter, chopped
pinch grated nutmeg

Method
1. For the watercress butter, in a bowl mix together the watercress, butter, shallot and mustard with a fork. Season well with freshly ground black pepper.
2. Preheat the oven to 220C/425F/Gas 7.
3. Slice the skin away from the salmon fillet leaving 2.5cm/1in still attached to form a flap.
4. Press a layer of the watercress butter between the skin and the flesh of the salmon.
5. Heat the oil in a frying pan, then place the salmon fillets in the pan skin-side down and cook for two minutes. Turn over and place in the oven for 3-4 minutes.
6. For the watercress mash, place the potatoes in a large pan, cover with cold water and season with salt. Cover and bring to the boil, simmer for 10-15 minutes or until tender.
7. Drain, return to the pan then tip in the chopped watercress and cover. Leave to stand for 1-2 minutes or until the watercress has wilted.
8. Mash the potatoes and watercress, then add the yoghurt or milk and butter.
9. Fluff up with a fork, add the nutmeg and season to taste with ground black pepper.
10. Heap the watercress mash in the centre of the plate and top with the salmon. Spoon the pan juices around and garnish with a sprig of watercress. Serve.