Preheat your oven to 180C/160C fan and line a tray with 12 regular baking cups
With a stand mixer, beat together the unsalted butter and light brown sugar until light and fluffy – I do this for 3-4 minutes so its super smooth and light as this makes it a moist recipe, and very light too!
Add the self-raising flour, cocoa powder, medium eggs, peppermint essence and vanilla extract and beat again - try not to over mix though as it'll make the cupcakes not so light & fluffy.
Fold through the chocolate chips and pour into the cupcake cases (I use an ice cream scoop so its even across all of the cupcakes!)
Bake in the oven for 15-20 minutes until cooked through
Once baked leave to cool
Beat the butter until smooth and supple for 3-4 minutes
Gradually add the icing sugar until buttercream is formed
Add the peppermint essence and Progel green food colouring to the colour you want and beat for at least 5-8 minutes or so until its smooth and fluffy