Stand 50 mini paper or foil cake (petit four) cases on a baking sheet. Put the mints in a polythene bag and beat with a rolling pin to break them into a coarse crumb.
Tip the mints into a bowl and add all the remaining cake ingredients. Beat with a hand-held electric whisk for about a minute until light and creamy. Divide the cake mixture between the paper cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 12 minutes or until risen and just firm to the touch. Transfer to a wire rack to cool.
Melt the plain and milk chocolate in separate bowls (see