Lightly MUDDLE mint (just to bruise) in base of glass. Add rum, lime juice and sugar. Half fill glass with crushed ice and CHURN (stir) with bar spoon. Fill glass with more crushed ice and CHURN some more. TOP with soda, stir and serve with straws.
When well made, this Cuban cousin of the Mint Julep is one of the world's greatest and most refreshing cocktails.