How to create:
- Preheat oven to 200°C (180°C fan) mark 6 and line a baking sheet with baking parchment. Peel the squash neck and slice evenly in half lengthways. Lay cut-side down on prepared sheet and brush with 1tbsp oil. Season and roast for 11⁄4-11⁄2hr, until tender. Set aside to cool.
- Meanwhile, make mushroom layer. Heat remaining 2tbsp oil in a large frying pan over medium heat and cook shallots for 5min, until softened. Turn up heat to high and add mushrooms. Cook, stirring occasionally, for 12-15min, until any liquid released by mushrooms has evaporated and they are golden brown. Add garlic, thyme and miso and cook for a further 2min. Remove from the heat.
- In a food processor or using a stick blender, blend cashews and stock until smooth. Stir this into mushroom mixture, check seasoning and set aside to cool.
- To assemble, line baking sheet with fresh baking parchment. Lightly flour a work surface and roll out 1⁄3 of the pastry to a 30.5 x 15cm (12 x 6in) rectangle. Spread over mushroom mixture, leaving a 1cm (1⁄2in) border around the edge. Lay on roasted butternut halves, making sure they join up neatly in the middle.
- Roll out remaining pastry as before until large enough to cover the assembled filling. Lay over the filling, trim edges and crimp to seal. Chill for 30min.
- Reheat oven to 200°C (180°C fan) mark 6. Brush Wellington with soya milk and cook for 50min–1hr, until golden brown and crisp. Leave to rest for 10min before transferring to a board or plate. Serve in slices.