Cover the chestnuts with water and simmer with the vanilla pod until the chestnuts are tender, about 2 hours. Add a little water if the chestnuts seem to be drying out. Cool slightly and whizz in blender, adding enough cooking liquor to make a purée.
Make the custard by beating the eggs and sugar in a bowl. Heat the milk until it is almost at boiling point and pour over the egg mixture. Return to the pan and cook carefully over a very low heat, whisking all the time, until the mixture thickens enough to coat the back of a spoon. Do not boil. Remove from heat, cool and fold in the whipped cream.
Melt the chocolate in a bowl over a saucepan of hot water. Combine the chocolate, chestnut purée and custard. Freeze in an ice cream machine or in a plastic container with a lid. To serve, decorate with grated chocolate, crystallised violets or, if you are feeling extravagant, crumbled marron glacé.
© 1984 All rights reserved. Published by Jon Croft.