Preheat oven to 180°C. Cream butter and sugar together. Add the Ready Egg, in three stages, beating continuously until light and fluffy. Beat in vanilla.
Sift flour, baking powder and salt together and fold into batter alternatively with the milk. Spoon 2/3 full into a muffin tray lined with cup cake cases. Bake for 15-20 minutes or until risen and lightly golden in colour.
Remove from oven and allow to cool on a wire rack.
For the icing:
Melt the chocolate in the microwave on High for 11⁄2 mins, stirring halfway. Leave to cool. Beat the butter and icing sugar in a large bowl until creamy. Beat in the chocolate.
Ice the cupcakes once they are cool.