Line a 20cm x 15cm tray with cling film or non-stick baking paper.
Put the biscuits in a plastic bag and smash them with a rolling pin until broken into small pieces, then tip them into a bowl. Add the chopped cherries, ginger and nuts, stirring to combine.
Melt the butter and golden syrup in a medium-sized saucepan. Set aside and keep warm.
Melt 500g of the white chocolate in a heatproof bowl set over a saucepan of simmering water on a low heat. Pour the chocolate over the melted butter and stir to combine, then pour it over the biscuit mixture and stir until all the ingredients are coated.
Spoon the mixture into the prepared tray and press down. Melt the remaining 200g of white chocolate and spread it over the top with a spatula. Leave to set in the fridge for 3 to 4 hours, then cut into pieces or squares. Store in a large Kilner jar at room temperature for up to two weeks.