In a pitcher, add the fresh mint leaves and simple syrup.
Gently muddle the leaves with a wooden spoon, being careful not to tear them.
Stir in the lemon juice and cold water.
Just before serving, add the ice and sparking water. Garnish with sliced lemon.
Notes
*Simple Syrup - In a medium saucepan, combine 1 cup white sugar and 1 cup water. Stir over medium heat until the sugar dissolves. Increase the heat and bring to a boil. Reduce the heat to medium and simmer for about three minutes. Chill thoroughly before using.