Heat oven to 200C/180C fan/gas 6. Line the bottom of a roasting tin with baking parchment. Brush 1⁄2 tbsp oil over the salmon skin and season. Place skin-side down in the tin and roast for about 15 mins until the salmon is just cooked through.
2 tbsp vegetable oil
2 small shallots, finely chopped
1 stick celery, finely chopped
½ glass dry white wine (optional)
1/2 pint vegetable stock
1 bay leaf
2 tbsp creme fraiche
180 g watercress
Place oil in a hot saucepan, add the shallots and celery and fry gently until soft. Add a sprinkle of sea salt along with the wine, stock and bay leaf and simmer for 5 minutes. Dollop in the creme fraiche and simmer for a few minutes. Remove the bay leaf, add the watercress, blitz with a hand blender and season to taste.