Preheat the oven to 200 C / 400 F / gas mark 6.
To prepare a large butternut squash: Cut the butternut squash at the base of the neck, before the more bulbous section where the seeds are. You can use the bulbous section another day so wrap up and place back in your fridge. Peel the remaining squash and cut in half lengthwise.To prepare two small butternut squashes: Cut off the necks and wrap up the bulbous part of them to use another day. Peel the necks then cut in half so that you are left with four discs. Transfer the butternut squash to a baking tray and drizzle with 2 tablespoon olive oil then season with salt and pepper.
Roast the butternut squash for 30 minutes or until tender.
In the meantime, in a large frying pan, heat a little oil over a medium heat. Add the diced shallots and fry for 5 minutes or until just becoming translucent.
Add a 2 tablespoon of olive oil to a frying pan on a medium heat.
Add the shallots to the pan and fry for 5-8 minutes until just translucent.
Next add both mushrooms and garlic to the frying pan and fry for 10-15 mins until the water from the mushrooms has evaporated.
Add the herbs and season to taste then fry for another 5 minutes.
Transfer half of the mushroom mixture to a food processor and pulse until it is more like a paste.
Add back to the rest of the mushrooms along with the chopped chestnuts and cranberries.
Leave this to cool completely before assembling.
In this time your butternut squash should have roasted. Remove from the oven and also leave to cool slightly.
To assemble the wellington, lay out the first sheet of pastry onto a baking tray that has been lined with baking paper.
Spoon roughly ⅔rds of the mushroom mixture down the centre of the puff pastry, as long and wide as your butternut squash.
Lay the butternut squash on top and then spoon the rest of the mushroom mixture around the butternut squash.
Lay the second sheet of puff pastry over the butternut squash.
Press down the edges to seal the pastry.
Trim off any excess and use these for decoration.
Make a series of cuts on top of the wellington to let any steam and moisture escape.
Brush the wellington with soy milk.
Bake in the centre of the oven for 35-45 minutes (still at 200 C / 400 F / gas mark 6) or until the pastry is golden brown.
Serve with your favourite roast dinner sides.