FOR THE CUPCAKES
Preheat the oven to 170ºC (fan)/190ºC/375ºF/gas mark 5.
Line either a muffin tin (for regular-sized cupcakes) or a mini cupcake tin with cupcake cases.
Melt the chocolate either using a bain marie or in a microwave but be very careful not to burn the chocolate! Leave to cool slightly.
Cream the butter and sugar together using an electric hand beater until pale and smooth. In a separate bowl and with clean beaters beat the egg yolks for several minutes. Slowly add the egg yolks to the creamed butter and sugar and beat well. Next, add the chocolate to this mixture and beat well.
Combine the flour, baking powder, bicarbonate of soda and salt. Combine the milk and vanilla in a jug. Add the flour mixture to the chocolate, butter and sugar, alternating with the milk and vanilla. Beat very well after each addition.
In a clean bowl, whisk the egg whites until soft peaks start to form. Carefully fold the egg whites into the main batter using a metal spoon. Do not beat or you will take all the air out of the cake.
Spoon the mixture out equally into the cupcake cases. You do not need to fill the cases with mixture, about two-thirds full will work best as the cakes will rise considerably in the oven.
Place in the oven and bake for between 20-25 mins for the regular size cupcakes or approx 15 mins for the mini cupcakes. Leave to cool in their tins for about 10 mins or so before placing on a wire rack to cool.
FOR THE MARSHMALLOW ICING:
Put the sugar, golden syrup and water into a pan and cook on a high heat for around 2 minutes. The mixture will thicken and turn a golden colour.
Whisk the egg whites until soft peaks start to form then keep beating while you slowly pour the hot sugar mixture into the bowl.
Continue beating at a higher speed until the mixture becomes thick, glossy and cool. Add the vanilla extract towards the end. Add a drop of your chosen food colouring at this point too, then mixed in on a high speed until the colour is evenly distributed.