Take two pounds more sugar than the weight of the orange. Rasp the naartje with a piece of glass (which prevents it tasting of steel) or a blunt knife; cut two slits across the bottom of the naartje, lay in water for two or three days, giving clean water every day. Boil the syrup, and when tepid pour it over the fruit; leave it for a night; preserve the next day very slowly, only letting it simmer. Repeat the process the third day, then bottle and cork well.