Cook the swede in a saucepan of boiling water for 15 minutes until tender. Drain and mash the swede with the measured milk and some seasoning. Spoon into a microwave-proof bowl, allow to cool, cover with clingfilm and chill until required.
Meanwhile, mix together the leeks, prunes, Brazil nuts and chestnuts in a large bowl. Mix in the breadcrumbs, egg and seasoning. Shape into 16 patties, arrange on a baking sheet, cover loosely and chill until required.
To make the sauce, mix the cornflour with a little water in a small bowl until smooth. Put the vegetable stock, cranberry sauce, vinegar, mustard and tomato purée in a jug. Add the cornflour mixture, stir well and chill.
When ready to serve, heat 2 tablespoons of the oil in a frying pan, add the patties and fry over a medium heat for 10 minutes, turning several times until browned and hot through. Add the remaining oil if needed.
Push the patties to one side of the frying pan, add the sauce mix and bring to the boil, stirring until thickened. Meanwhile, reheat the swede in a microwave on full power for 2½–3 minutes until piping hot. Stir, then spoon on to serving plates and top with the patties and sauce.