Set out butter and milk to come to room temperature.

Preheat oven to 350F/160C (fan)/180C/gas mark 4.  Line a 12-hole muffin tray with cupcake cases.

Break dark chocolate into pieces.  In a heatproof bowl, heat over a saucepan of barely simmering water.  Stir until melted.  Then set aside. 

In a bowl, cream (with an electric mixer) butter, sugar, and orange zest.  Add eggs and beat.

Combine flour, baking soda, baking powder, and salt. 

Mix milk and orange juice together.

Add the chocolate to the creamed mixture.  Beat on  low speed or by hand.  The batter will still be streaky.  Add a third of the flour mix.  Beat again.  Add half the juice/milk mix.  Beat.  Repeat until all ingredients are well incorporated.

Carefully spoon the mix into cupcake cases about 2/3 full.  Bake for 28-30 minutes.

Remove from the oven, leaver to cool for 10 minutes.  Cool completely on a wire rack.  Once completely cool, frost with chocolate buttercream and decorate with orange zest or sugar flowers.