Slice a lime into eight slices and put two into a glass. Pour the tablespoons of cane sugar over it, and mash these together - if you don't have a long shafted mortar, the end of a ladle can be used. Pour coarsely crushed ice-cubes to the brim of the glass, and fill it with the Havana Club white rum. Serve with medium sized straight straws. Vary the lime / cane sugar ratio according to personal taste.