2 shots espresso, chilled
Simple syrup (see Cook's Note)
Twist of lemon or orange peel
4 to 6 ounces cold sparkling water
To make simple syrup, combine equal parts sugar and water in a small saucepan and bring to a boil over high heat, stirring once or twice to dissolve the sugar. Remove from the heat and let cool. Refrigerate, covered, indefinitely.