In a large bowl, combine all ingredients and whisk until smooth. Refrigerate for 30 minutes.
Preheat oven to 180°C/350°F. Using a pastry brush, grease all the moulds of the madeleine tins with 2 tablespoons melted butter.
Remove the madeleine batter from the fridge and evenly fill the deepest part of each mould with a spoonful of the mixture. Bake for about 8-10 minutes or until cake springs back when lightly touched. Try not to overcook as they will be dry.
Remove from oven and allow to cool for a couple of minutes before removing from the moulds (give the pans a little shake and madeleines should fall out).
For the rum and raisin chocolate, combine all ingredients together in a microwave-safe bowl and microwave in short bursts, stirring until completely melted and smooth. Take care not to overcook the chocolate.
When the madeleines have completely cooled, dip in the rum and raisin chocolate and enjoy! These are best eaten almost immediately after they have cooled.