Preheat the oven to 180°C (160° fan) | 350F | gas 4 and brush a 27 x 14 cm | 10-inch x 5-inch silicone loaf mould with butter.
Beat the sugar and milk into the mashed potato in a large mixing bowl. Beat in the flour, then fold in the pear, white chocolate and half of the hazelnuts.
Scrape the mixture into the prepared loaf mould and sprinkle the rest of the hazelnuts on top.
Leave the icing to set for 1 hour before threading with string and dusting with a little icing sugar.