Preheat you oven to 350°F (175C/155C Fan) and line a 12-hole cupcake pan.
Place the orange juice, milk and vanilla extract in a small jug and set aside.
In a large mixing bowl, cream together the butter, sugar and brown sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Then add the orange juice mixture and orange zest. Beating to blend together.
Sift the flour, cocoa powder, baking soda and salt into the mixing bowl and stir thoroughly with a spatula until just combined. Be sure there are no remaining pockets of flour.
Spoon out into prepared cupcake tray and bake in the centre of the preheated oven for about 22 minutes - start checking around 20 minutes and remove once a skewer inserted in the centre of one of the middle cupcakes comes out clean.
Allow to cool on a wire rack and frost with ganache or chocolate buttercream and top with citrus peel.