Pre-heat oven on gas mark 4, grease and line two 8 inch cakes tins. Mix the cocoa powder with the hot water and leave to cool for a minute.
Beat the butter and caster sugar together until combined then add the eggs one at a time. Once all the eggs are mixed in, add the chocolate mixture and flour then beat again until incorporated.
Melt the milk chocolate and add that to the mixture along with the peppermint essence then mix until incorporated. Separate the mixture evenly between the two tins.
Put in the over for about 25 minutes until a skewer comes out clean. Once cooked, remove and leave them in the tin to cool for a bit then transfer to a wire rack to cool completely.