Preheat the oven to 180°C, gas mark 4. Put the tomato, onion and half the garlic in a liquidiser and process to a purée. Heat 1 tbsp oil in a frying pan, add the purée and boil for 2-3 minutes until thick. Stir in the beans, and add either the liquid from the cans, or the vegetable stock if you prefer. Add the chestnuts, paprika and bay leaf. Bring to the boil, reduce the heat and cook gently for 10 minutes.