1Preheat oven to moderate, 180 C. Grease 6 holes of a mini (1-cup) bundt tray. Prepare cake mix following the packet instructions. Divide batter between three bowls.
2Tint each bowl of batter with food colouring to achieve different shades of pink. Spread the palest cake batter over bases of prepared holes. Top with the next shade of cake batter. Bake 25 mins or until a skewer inserted into centre comes out clean. Stand in tray 10 mins, then turn out onto a wire rack to cool completely.
3Meanwhile, in a medium heatproof bowl, combine icing sugar, juice and water. Place bowl over a small saucepan of simmering water. Stir until icing is smooth. Remove from heat.
4Drizzle cakes with icing. Decorate with cachous and sugar crystals.