Pre-heat the oven to 160C Fan/180C/350F/Gas Mark 4 and grease and line a 2lb loaf tin
Mix together the butter and caster sugar, ideally using an electric mixer, until light and fluffy
Add the orange extract, eggs and milk and whisk in until smooth
Whisk in the flour, baking powder and cocoa powder until fully combined
Fold in the chopped up Terry's Chocolate Orange pieces
Pour the mixture into the loaf tin and bake for an hour, or until a thin skewer inserted in the centre comes out clean. Leave to cool fully
To make the buttercream, use an electric mixer for the best results. Mix together the butter, cocoa powder and icing sugar until they start to combine, then add the orange extract and milk and mix until smooth. You can add more milk if the buttercream is too stiff
Put it into a piping bag and pipe it onto the loaf cake, or spread on with a spoon or spatula
Decorate with the remaining Terry's Chocolate Orange pieces and some sprinkles too if you like!
Store in an airtight container in a cool place and eat within 3 days