Place the mandarins into a saucepan and cover with cold water, then bring to the boil. Completely drain and then repeat the process two more times. Once complete, allow mandarins to cool to room temperature.
Preheat oven to 180 degree C. Place cupcake papers into muffin trays and set aside.
In a food processor, process macadamia nuts until finely chopped and place in a small bowl. Halve the mandarins an discard the seeds. Process the mandarins until they are pulp.
Beat butter and sugar with an electic mixer until light and fluffy. Beat in eggs, one at a time. Pour mixture into a large bowl and stir in polenta, baking powder, nuts and mandarin pulp. Then spoon into cupcake papers. Bake for about 35 minutes. Stand for 5 minutes before turning out onto a wire rack to cool.
Sift icing sugar into a bowl and stir in the mandarin juice and butter. Spread evenly over cooled cupcakes and decorate!