Pour the stock into a large saucepan and bring to the boil. Add the polenta, and stir continuously over a medium heat for 3-4 mins until thickened and just coming away from the edges of the pan. Add the olives, tomatoes, oil and most of the parmesan, and stir for a further minute until well combined. Season.
Spoon the polenta mixture onto a lined swiss roll tray or baking sheet. Place another sheet of baking parchment on top and roll out to 1cm thick, then remove the top sheet of parchment and scatter with the remaining parmesan. Leave the polenta to cool at room temperature for 1 hr to set. Alternatively, if you’re making it ahead, leave to cool and chill for several hours or overnight.
Once the polenta has set, heat the oven to 200C/180C fan/gas 6. Cut or stamp the polenta sheet into shapes of your choice, and arrange on a baking tray lined with parchment. Bake for 25-30 mins until golden brown and crisp, and serve warm. Will keep for up to a day in the fridge.
