Alaska Salmon Side with Country Garden Herb Sauce

Ingredients

• 1 side wild Alaska salmon
• 4 tbsp olive oil
• Finely grated zest and juice of 1 lemon
• 30g butter
• 1 small onion, very finely chopped
• 120ml dry white wine
• 30g watercress, finely chopped
• 1 tbsp chopped fresh chives
• 1 tbsp chopped fresh marjoram, oregano or parsley
• 300g crème fraiche
• Salt and freshly ground black pepper