Preheat the oven to 200C.

Heat a little bit of oil in a large frying pan, add the onion and garlic and sweat over a medium heat for about 6-8 minutes.

Add the spinach, it will look like a lot, but it will soon shrink up. Cook until it wilts. Season with salt and pepper, then take it off the heat and leave to cool completely.

When it’s cooled, add the cream cheese and wholegrain mustard to the spinach and mix it well.

Roll out the sheet of puff pastry. Spread half of the spinach mix on one end leaving a border. Pop the salmon on top then spread the remaining spinach mix over the top.

Fold the pastry over and press down to seal the edges. Ensure there are no air pockets inside.

Cut away any excess pastry. Brush the pastry with egg yolk then score diagonally across the top.

Bake it for 30-35 minutes until it’s golden and crisp. Take it out of the oven and leave it to rest for at least 5 minutes before carving.