Add the milk chocolate to a microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth. Leave to cool slightly.
In a large bowl, beat the cream cheese until smooth. Gradually mix in the icing sugar until smooth and combined.
Stir in the melted chocolate and vanilla until fully combined. Cover and refrigerate/freeze for at least 2 - 3 hours or overnight until firm.
Once firm, roll the mixture into tablespoon-sized (0.7oz) balls, and place them on a baking tray lined with parchment or wax paper.
The mixture will feel quite sticky and melty, but it's fine. Lightly coat your hands in cocoa powder or icing sugar to make the process easier.
Freeze for 1 hour.
Dip each ball into the dark chocolate and place back onto the baking tray. The chocolate coating should set quickly as the balls are cold from the freezer.
Drizzle the truffles with white chocolate. Keep refrigerated until ready to serve.
Video
Notes
Truffles can be kept in an airtight container, layered between parchment or wax paper, in the fridge for up to 1 week. They also freeze well for up to 2 months. Thaw overnight in the fridge.