Wash the lime and cut off both ends. Cut the lime into 8 or 9 pieces and remove the central white part responsible for the bitterness.
Place the pieces in the glass and pour a good tablespoon of sugar. Crush firmly into the glass with the powdered sugar until the juice is extracted as completely as possible.
Cover the lime-sugar mixture with a good layer of crushed ice or simple ice cubes (close to the rim), then level it to a finger from the rim.