Preheat your oven to 180c (160c fan) and line a 12 hole muffin tin with cupcake cases.
Cream the butter and sugar together. Slowly add the eggs, one at a time. Add the vanilla extract and zest of one orange, mix until combined.
In a separate bowl mix the flour, baking powder, salt, cocoa powder and fennel seeds together.
Fold in the dry ingredients to the wet.
Fill each cupcake case and bake in the oven for 12 - 15 minutes.
For the orange buttercream frosting
Beat the butter and salt together until smooth. Add half the icing sugar, half of the juice of one orange, 1 tbsp golden syrup, the vanilla extract and continue to mix. Then add the rest of the icing sugar, the rest of the juice of the orange, 1 tbsp golden syrup and mix until it's thick and creamy.
Once the cupcakes have cooled, pipe the buttercream frosting onto your cupcakes.
Freeze any leftover buttercream and use for your next batch!