Watercress Sauce

• 55 g/2 oz watercress, any thick stalks removed
• 2 tbsp chopped chervil

Bring a small saucepan of unsalted water to the boil. Add the watercress and blanch for 30 seconds, then immediately drain and refresh under cold running water. Squeeze to remove as much water as possible.

Put the watercress, chervil, dill and parsley in a mini food processor and process until finely chopped.

Transfer to a bowl, stir in the lemon juice and crème fraîche and seas