In a bowl, combine the mascarpone, spinach, parsley, dill, shallot, garlic and lemon zest.

Lay one sheet of puff pastry onto a sheet of baking paper. Scatter the breadcrumbs and pistachios over the centre approximately the same size area as the size of the salmon.

To even out the thickness, look at the thinner side of the salmon and slice a strip off, so that you can sit it on top to make it around the same thickness as the thick end (see step by step images in post if you need).

Season the flat side of the salmon with salt and pepper, then spread over half of the mascarpone mixture. Lay it mascarpone side down onto the breadcrumbs mixture.

Sprinkle the top with salt and pepper, then place that thin offcut on top of the thin side of the salmon. Spread the remaining mascarpone mixture over the top. It can be a bit fiddly trying to spread it on over the offcut piece but it’s worth doing.

Lay the second sheet of puff pastry over the top, pressing out the air as you join all the edges. Trim so that you have a 2cm border all the way round, then crimp the edges with your index fingers and thumb.

Using the rounded tip of a teaspoon, press a fish scale pattern all over the top then poke 4-5 small holes in the top of the pastry with the tip of a sharp knife to allow steam to escape.

Brush the egg wash over the top of the pastry then transfer the wellington to a large baking sheet using the baking paper to lift it.

Bake for 30-35 minutes or until a thermometer reaches 63°C/145°F in the thickest part of the salmon. The edges will brown quicker than the centre, so after 12-15 minutes, take it out and cover the edges with foil, then return to the oven, turning the tray so that it cooks evenly.