Traditionally, this drink was served with cold water and a cube of sugar because absinthe is very bitter. The sugar was placed on a decorative, nearly flat, slotted absinthe spoon, and water was drizzled over it into the glass, turning the liquid a milky greenish white. Modern recipes use club soda as opposed to the original mineral water.
Pour absinthe into a mixing glass half filled with crushed ice. Place the sugar cube on top of the ice. Slowly drip club soda on the sugar cube until it is completely dissolved. Mix well then strain into a chilled cocktail glass.
If you have an absinthe spoon - Place the absinthe spoon across the rim of the glass, and place the sugar cube in the bowl of the spoon. Slowly drip the water over the sugar to melt the sugar into the glass.
Note: Pernod or Herbsaint are sometimes used as substitutes.