Stir together lemon juice and sugar in a 3-quart pitcher until sugar is dissolved. Add water and stir until combined. Garnish with additional lemon slices and mint, if desired. Serve over ice in glasses.
Notes
If superfine sugar is not readily available where you shop, you can place regular granulated sugar in a food processor to great that fine texture.
You can refrigerate the lemonade if not serving immediately; stir before serving.
The lemonade can be stored in the refrigerator for up to 1 week.