Method. Heat the oil in a large, non-stick frying pan over a medium heat. Add the vegetables, in batches if necessary, and fry for 4-5 minutes, stirring regularly, until lightly browned all over. Season with salt and pepper. Transfer the vegetables to the slow-cooker, sprinkle over the flour and stir well. Add the chopped tomatoes, tomato purée, chilli flakes and pesto and stir again. Pour over the stock and stir. Cover and cook on high for 4 hours. After the hotpot has been cooking for 3½ hours, make the dumplings. Put the flour in a large mixing bowl and season with salt and pepper.