Put the long grain rice in a pot, cover with cold water and bring to a boil. Reduce the temperature, cover and simmer gently for 15 min or possibly until the water is absorbed. Stir in the butter and fine granulated sugar.
Grease a 600 ml heatproof custard dish. Cover the bottom and sides of the baking dish with a thin layer of rice, pressing it smooth with the back of a spoon.
Mix the dried and candied fruits and walnuts and press this mixture into the long-grain rice.
Spread a wider layer of rice on top and fill the center with the chestnut puree. With the remaining long-grain rice, cover the puree completely and enclose it by pressing a little on the long-grain rice.
Cover the baking dish with folded parchment paper and foil and secure with string. Place in a steamer or pot half filled with hot water. Cover and steam for 45 min. Stand 10 min.
Before serving, gently heat the water and orange juice in a small saucepan. Add the light brown sugar and stir through. Allow the syrup to bubble.
In a small baking bowl, mix the cornstarch with the cold water and stir into the boiling syrup. Cook for 1 minute.
Lift the pudding onto a serving plate. Pour the syrup over it, cut into portions and bring to the table.