Candied walnuts can be nibbled as sweets or used to decorate cakes and tarts. The candied walnuts last several weeks in a sealed jar or can. Pour the water into a pan. Add the sugar and bring to the boil stirring. Add the walnuts and cook at high temperature until the sugar is dry. Stir constantly with a wooden spoon. Switch down to medium temperature and stir the walnuts until the sugar melts again. Add a little butter and stir the walnuts until they caramelise. Immediately cut the candied walnuts on baking paper or a greased baking tray with a knife. Candied walnuts taste warm or cold.