Pour absinthe into an absinthe glass.
Place a slotted absinthe spoon over the rim of the glass and set a sugar cube on top of the spoon. (Sugar is optional so always ask for the guest’s preference. If they don't want their absinthe sweetened: omit the spoon and sugar cube).
Using an absinthe fountain or water carafe, slowly pour or drip ice cold water over the sugar cube into the glass.
As the dripping water dissolves the sugar cube; watch the layer of undiluted absinthe rise to the top of the glass. When the mixture is completely cloudy, the drip should be ready. Stir, taste for strength and adjust with more water if necessary.