Heat the oven to 190C/fan 170C/gas 5. Scoop out some flesh from the neck of the butternut squash, ensuring you leave a shell approximately 2cm thick. Finely chop the scooped out butternut flesh and put in a frying pan with 1 tbsp of the vegetable oil, onion, celery, carrot, garlic and a pinch of salt. Cook gently for 10 minutes until the vegetables have softened. Stir in the breadcrumbs, apple, sage and some seasoning. Cool a little then mix in the egg yolk.
Season the butternut squash shell and spoon the stuffing into the cavity. Carefully put the two halves of the butternut back together to reform the squash and tie with string at intervals to secure it. Put into a roasting tray and use scrunched up foil on either side so it doesn’t roll over. Drizzle well with the remaining vegetable oil, season again and roast for 1 hour 30 minutes-1 hour 45 minutes or until the squash is tender but still holding its shape.
To make the sauce, put the cider into a pan and boil to reduce by ½. Pour in the double cream then simmer until thickened. Stir through the wholegrain mustard and season.
When the butternut is ready, blanch the kale in a large pan of salted boiling water for 1 minute until wilted, drain really well then toss with the extra-virgin olive oil and seasoning.
Serve the butternut with the kale scattered with pumpkin seeds, and sauce on the side.