Rinse and dry oranges. Peel rind into thin strips using a sharp vegetable peeler, being careful to avoid any white pith. Save oranges for other uses.

Combine zest and alcohol in a glass jar; cover with a tight-fitting lid. Set it aside in a cool, dark place for four days (liqueur should be a bright orange and orange peel should be pale). Strain liqueur through a fine-mesh strainer into a clean bowl; discard solids.

Combine sugar and water in a medium saucepan; stir over medium heat until sugar dissolves and syrup is clear (do not boil). Remove from heat and let cool.

Once cooled, combine syrup and liqueur; stir well. Carefully pour into clean bottles; seal with corks or screw tops. Set aside for two weeks at cool room temperature to allow flavors to mellow. Chill before serving.