Salmon En Croute with Herb Mayonnaise

Ingredients

• Oil (for greasing)
• 1 large leek (halved lengthways and finely chopped)
• 2 handfuls watercress (tough stems discarded & roughly chopped)
• 125ml/4fl oz crème fraiche
• 650g/1lb 7oz thick salmon fillet (bones and skin removed)
• 320g/11¼oz ready-rolled puff pastry
• Flour (for dusting)
• 1 egg (lightly beaten)
• Sea salt and freshly ground black pepper
• .
• Herb Mayonnaise:
• 100ml/3½fl oz mayonnaise
• Juice of 1 small lemon
• 3 tbsp finely snipped chives
• 3 tbsp chopped dill

Instructions

1. Preheat the oven to 200°C/400°F/Gas 6 and lightly grease a large, non-stick baking tray.
2. Steam the leek for 5 minutes or until tender. Leave until cool enough to handle then, using your hands, squeeze out as much water as possible. This will prevent the pastry becoming soggy during baking. Put the leeks in a mixing bowl and stir in the watercress and crème fraiche. Season the mixture generously with salt and pepper.
3. Roll out the pastry slightly on a lightly floured work surface into a large rectangle. Lay the salmon lengthways down the centre of the pastry, then spoon the leek mixture over the top in an even layer.
4. Make diagonal cuts, 2.5cm/1in wide, in the pastry either side of the salmon; if you cut away the pastry corners, this makes it easier to plait. Begin to plait the pastry taking one of the strips and folding it over the filling then taking one from the other side and folding that over. Continue until you have plaited the pastry all the way down to make a long log shape.
5. Using 2 spatulas, carefully transfer the salmon parcel to the prepared baking tray. Glaze the top with egg and bake for 30–35 minutes until golden and the pastry is cooked through.
6. Meanwhile, mix together the mayonnaise, lemon juice and 1 tablespoon water to loosen the mixture, then stir in the herbs. Serve the salmon in slices with a good spoonful of the mayonnaise by the side.