1. Put the onions, garlic, carrots, celery and 284ml / ½ pint of the vegetable or beef stock in a large heavy-based saucepan. Cover the pan and bring to the boil.
2. Continue boiling for 5-10 minutes, then uncover the pan, reduce the heat and simmer for about 20-30 minutes, until the vegetables are tender.
3. Add the Quorn mince and stir well. Add the remaining stock, tomatoes, tomato puree, herbs, seasoning and sugar. Bring to the boil, then reduce the heat and simmer gently for about 1 hour, until the sauce is reduced and richly coloured.
4. Cook the spaghetti in boiling, lightly salted water until tender and al dente ("to the bite"). Drain well and divide the spaghetti between 4 serving plates. Top with the bolognese sauce and serve sprinkled with chopped parsley.