Lemon glacé icing
1.Preheat oven to 180°C. Line eight holes of 12-hole (1/3-cup/80ml) muffin pan with paper cases.
2.Beat butter, rind, sugar, eggs, sifted flour and milk in small bowl with an electric mixer on low speed until ingredients are combined. Increase speed to medium; beat until mixture has changed to a paler colour. Drop ¼ cups of mixture into paper cases.
3.Bake about 20 minutes. Stand cakes in pan 5 minutes before turning, top-side up, onto wire rack to cool.
4.To make lemon glacé icing, sift icing sugar into small heatproof bowl; stir in butter and enough of the juice to make a thick paste. Stir over small saucepan of simmering water until icing is spreadable. Spread cold cakes with icing; stand until set.
5.Fill a small piping bag without a tube with the warm chocolate; quickly drizzle chocolate backwards and forwards over the cake tops. Sprinkle cakes with cachous before chocolate sets.