Extra Special Fluffy Chocolate Buttercream

I have just discovered this way of making buttercream, and it is so good that I had to share it!

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   Sift the flour and cocoa powder into a small saucepan. Add the milk and using a whisk or wooden spoon, whisk or beat together over a medium heat until it forms a thick paste (about a minute and a half). Remove from the heat, spoon into a small bowl and cover with cling film, pressing it down onto the surface of the paste so that a skin does not form. Put this into the fridge for at least 10 minutes, until cool to the touch.
   
   Melt the chocolate in a glass bowl over a pan of simmering water, or in a microwave and leave to cool slightly.
   
   With an electric hand whisk, beat together the butter and icing sugar until light and fluffy. It may seem dry at first, but keep going, and the texture will change. Beat in the chocolate paste until the buttercream lightens in colour and becomes fluffy in texture. It will look a bit like a pale chocolate mousse. Add the melted chocolate and keep beating until smooth.