BBC Food - Recipes - Brown trout with crayfish and watercress sauce

Ingredients

• 2 tbsp sunflower oil
• 1 onion , peeled and roughly chopped
• ½ fennel bulb, thickly sliced
• 1 celery stick, thickly sliced
• 1 medium carrot , thickly sliced
• 1 bay leaf
• small bunch fresh thyme
• 12 crayfish or large raw prawns, shells on
• 1 heaped tbsp tomato purée
• 200ml/7fl oz dry white wine
• 300ml/10fl oz water
• ½ tsp flaked sea salt
• 4-5 tbsp double cream
• 1 tsp sunfower oil
• 25g/1oz butter
• 4 x 200g/7oz brown trout or sea trout fillets, pin-boned, skin left on
• 1 bunch watercress , leaves trimmed
• flaked sea salt and freshly ground black pepper