Heat the oven to 180C/350C/Gas 4

Grease and line the base of two 17.5cm (7in) sandwich tins

Blend the cocoa powder in a bowl with the hot water and leave to cool.

Put the butter, sugar, flour, baking powder and eggs in a large bowl, add the cooled chocolate mixture and, using an electric mixer, beat until smooth.

Divide equally between the two tins, smooth the top, and shake or tap the tins to evenly distribute the mixture.

Bake for 20-25 minutes until the sponges start to come away from the sides of the tins and spring back when the centre is pressed.

Leave in the tin for 3-4 minutes, then turn onto a rack to cool. The cakes must be completely cool before icing, and even better if you can leave it till the next day.

Put the butter in a large bowl and beat until soft.

Gradually add the icing sugar until it starts to come together then add the milk and flavourings. Beat again until you have a spreading consistency.

Add the green colouring paste and beat until you have a consistent pale green colour.

Finally add the chocolate and finely chopped fresh mint leaves and mix so they are distributed throughout the buttercream

This quantity will fill the sandwich cake and cover the top and sides. No further decoration is really needed but you could add some chocolate curls and as sprig of fresh mint.