To Coat the Madeleines with Chocolate

1. Place the chopped white chocolate into a heat proof bowl.  Microwave for 30 seconds, then take it out to stir.  Then microwave it for a few 15-second bursts until completely melted.  In order to keep it liquified, place the bowl in a big bowl of warm water (otherwise it re-sets very quickly).  
2. Decide how many colours you want for your chocolate shell bases and then take a small amount of white chocolate for each and colour using oil-based food colouring.  
3. Next, make sure the madeleine moulds are warm.  I use a hair dryer to do this.  
4. Spoon about 1 tablespoon of melted/coloured white chocolate into each cavity of the madeleine pan. 
5. Place a (cooled) madeleine on top of the chocolate. Gently press and wiggle slightly so the chocolate spreads evenly across the shell.
6. Leave the madeleine sitting in the pan and repeat for the rest.
7. Transfer the whole pan to the freezer for 15 minutes, or until the chocolate is completely set.
8. Once set firm, simply push the madeleines out of the pan—the bottoms should be coated in a crisp layer of chocolate.

To Decorate the Madeleines with Royal Icing

1. In a mixing bowl, combine icing sugar and meringue powder.
2. Add a few tablespoons of water and beat until the mixture becomes glossy, shiny, and nearly doubles in volume.
3. Adjust the consistency as needed:  add a little more water to thin out or add extra icing sugar to thicken.
4. Divide the icing into bowls and mix in gel food colouring to achieve your desired colours.
5. Once your royal icing is ready, transfer it to piping bags and begin decorating your madeleines as desired.