Put the chocolate in a medium heatproof bowl. Tip the milk, sugar and vanilla into a small saucepan, then bring to the boil over a medium heat, stirring occasionally.
Pour the hot milk mixture over the chocolate, leave to sit for 1 min, then stir until the chocolate has melted and the mix is smooth. Cover and chill for 4 hrs until set.
Roll teaspoons of the mixture into balls using your hands, then transfer to a small baking tray or plate – you may like to wear gloves. You should have about 20 balls.
Put the cocoa powder on a shallow plate, and roll the chilled truffles in it until well-coated, tapping off any excess, if needed. Chill until you’re ready to gift. Will keep in the fridge for up to four days.