Pour the absinthe into an absinthe glass. If desired, place a slotted absinthe spoon over the rim of the glass and set the sugar cube on top of the spoon. Using an absinthe fountain or water carafe, slowly pour or drip ice-cold water over the sugar cube into the glass until the mixture is completely cloudy. Stir, taste for strength and sweetness, and adjust with more water or sugar if necessary.(An excellent selection of traditional absinthe glassware, spoons and fountains is available at lamaisondabsinthe.com.)