Preheat the oven to Gas 6, 200°C, fan 180°C. Line a 24-hole mini muffin tray with paper cases.
In a large bowl, sift together the flour, cocoa, baking powder, bicarbonate of soda and sugar. Stir in the raisins and half the chocolate chips.
Mix the milk, oil and egg together with a fork, then pour into the dry ingredients and mix together to form a runny batter.
Divide the mixture between the paper cases then scatter over the remaining chocolate chips. Bake for 15 minutes or until risen and firm to touch. Transfer to a wire rack to cool.
Melt the white chocolate in a bowl placed over a pan of hot water. Spoon the melted chocolate over the muffins to resemble a Christmas pudding, then decorate with silver balls and leave until the chocolate has set.