Preheat the oven to 180°C, fan 160°C, gas 4. Put the butter and sugar in a large mixing bowl and beat until pale and fluffy. Whisk in the egg.
In a separate bowl, combine the flour, cocoa and almonds. Mix in the milk and add to the butter and sugar mixture. Spoon into 12 cupcake cases then bake for 20 minutes or until a skewer inserted into the centre comes out clean. Leave to cool completely.
To make the icing, gradually mix the icing sugar into the butter and whisk until light and creamy. Add the milk and chocolate and whisk well. Smooth onto the cupcakes with a small spatula and sprinkle with the flaked almonds.