An excellent and fascinating history of this can be found at http://www.oxygenee.com/.
A new method of sweetening Absinthe has recently become popular. Once the absinthe is poured (now as a shot), a small amount of sugar in a spoon is dipped into the glass, soaked, and withdrawn. The sugar is then set on fire until it melts and caramelizes, and then is stirred into the drink. Cold water is then added to the drink to put out the alcohol fire.