Mix together all of the shortbread ingredients to form a dough. Knead gently until smooth. Roll the dough into a cylinder, making sure each end is flat, and wrap in cling film, twisting the ends to form a seal. Refrigerate for at least 45 minutes.
Meanwhile, preheat oven to 180oC. Remove the dough from the fridge and slice into 0.75cm rounds. Remove the cling film from around the shortbread edges and arrange on a greased baking sheet.
Bake for 10-13 minutes. Remove from the oven when the shortbreads are pale gold at the edges. Immediately sprinkle over grated Parmigiano Reggiano and rosemary.
Cool before serving.