In a large bowl, mix the ginger nut biscuits, ground almonds and ground ginger. Add the condensed milk and mix thoroughly until combined.
Line a couple of baking trays with some greaseproof paper. Take a small amounts of the mixture and roll into balls (or use a melon baller), before placing onto a tray. Once the whole mixture is rolled into balls, return to the fridge for at least 30 minutes.
Melt the white chocolate over a bain-marie or in short bursts in a microwave. Coat each ball with the chocolate before returning to the tray. Top each truffle with a little chopped crystallised ginger if you wish. Allow the truffles to set in the fridge for 1-2 hours.