Put the dry ingredients into a mixing bowl - flour, sugar, baking powder, cocoa powder and butter (treat butter as 'dry' for our purposes). Mix until you have an even sandy consistency.
Measure out the milk, egg and vanilla in a jug and whisk well. Drizzle into the flour whilst mixing, until you have a smooth batter/mixture. Zest both oranges and place half the zest into your mixture. Reserve the other half for decorating. Throw in the handful of choc chips, mixing for a couple more seconds, then stop the mixer and clean down the blade.
Spoon evenly into 12 cupcake cases and bake at 170°C for 20 minutes until they bounce back to the touch.
Cool on a wire rack and in the meantime make the icing by mixing the icing sugar, butter, cocoa powder, milk and juice together for several minutes until very light and fluffy.
Pipe the icing on top of the cakes using a reusable piping bag and large star nozzle and sprinkle with the orange zest to decorate. No-one will know these are gluten free cupcakes as they are so scrummy!