Place the flour, sugar, carrot, orange zest, half the walnuts, the mixed spice and the baking powder in a large bowl and combine. In a separate bowl, gently beat together the golden syrup, sunflower oil and eggs.
Preheat the oven to 180°C/fan 160°C/gas mark 4. Line a cupcake tin with 12 cases.Pour the wet ingredients into the dry and mix well. Spoon into the paper cases and bake for 25 minutes. Cool completely.
Meanwhile, whisk together the butter and icing sugar until soft. Stir in the cream cheese and whisk until combined. Spoon into a piping bag with a star-shaped nozzle. Pipe the icing on to the cooled cupcakes and decorate with the remaining walnuts, the extra carrot strips and the mini eggs.