This is the traditional method of making a mint Julep.  Muddling or bruising the mint with the sugar allows more of the oils from the mint to be released.  For convenience sake however, many people now use Simple Syrup instead.

For each serving;

Place 1 teaspoon sugar in the bottom of a Collins glass or Julep cup.  Add 3 or 4 fresh mint leaves and muddle until the mint is well bruised and the sugar somewhat dissolved.  Fill the glass with crushed ice, then pour in about 2 ounces of Bourbon.  Add a straw and garnish with a sprig of ming.