150g mascarpone or cream cheese
1 bag watercress, spinach and rocket, about 120g
500g all butter shortcrust pastry block
500g piece salmon fillet, skinless
1 egg, beaten
Heat the oven to 200C
Put the mascarpone or cream cheese in a food processor with the watercress, spinach and rocket and whizz the lot until you have a creamy green purée. Season well.
Roll the pastry out so you can wrap the salmon in it completely (just a bit thinner than a £1 coin) and lay it on a buttered or oiled baking sheet (it will hang over the edges).
Put the salmon in the middle. Spoon half of the watercress mixture onto the salmon.
Now fold the pastry over into a neat parcel (the join will be at the top, so trim the edge neatly), making sure you don't have any thick lumps of pastry as these won't cook through properly. Trim off any excess as you need to.
Make 3 neat cuts in the pastry to allow steam to escape and make some decorations with the off-cuts to disguise the join if you like. Brush with the egg glaze.
Bake for 30 minutes or until the pastry is crisp and browned. To test whether the salmon is cooked, push a sharp knife through one of the cuts into the flesh, wait for 3 seconds then test it against the inside of your wrist; if it is hot, the salmon is cooked.
Serve with the rest of the watercress purée as a sauce.