1. Preheat the oven to 180C/350F/Gas Mark 4.
2. Fry the onion, celery, mushrooms, and garlic in a little olive oil until soft and just beginning to colour.
3. Steam or boil the carrots and sweet potato until soft.
4. Place all the ingredients except the nuts and wheat gluten into a food processor and blend until smooth.
5. Add the cashews and chestnuts in a food processor and pulse until coarsely chopped.
6. Remove from the food processor and add the wheat gluten.
7. Mix all the ingredients together in a large bowl.
8. Press into a greased 900g/2lb loaf tin or ring mould.
9. Cover with foil and bake in the preheated oven for 1 hour.
10. Remove the foil and bake for a further 10 minutes.
11. Leave to stand in the tin for 10 minutes before turning out.