Roast the chestnut flour, stirring constantly, until it turns dark brown.
Mix with vegetable oil or butter in the pan (roux).
Add the stock and tomato purée and turn the heat down as soon as it comes to the boil.
Pour in the stock and simmer for approx. 30 mins. Add the tomato purée and cook for a further 15 minutes.
Add the chestnut flakes, stir well and serve.