Place 5 frozen spinach cubes into a sieve and run warm water over the top until defrosted then drain out excess water.
Heat the oil in a large pan fry the leeks for 5 minutes then add the garlic and thyme fry for a minute, add the chestnut mushrooms and fry for another 10 minutes
take the mixture off the heat and stir in the crumbled chestnuts and salt and pepper to taste
In the same pan fry then portobello mushroom slices for a few minutes each side until golden. On some cling film or bees wax wrap place half the mushroom mixture in a rectangle about 1cm high then place the portobello slices lengthways along the entire log.
Add the rest of the leek mixture on top and top with the spinach, wrap and place in the fridge for an hour.
Preheat the oven to 200c
place the rolled out pastry on a lined baking tray
place the filling in the middle of the pastry sheet
Wrap the pastry over the filling and press the ends together to seal
Use any excess pastry to decorate. brush with egg yolk or plant milk and bake for 30 minutes until golden