In a medium saucepan, combine 2 cups of water and 1 cup of brown sugar. Heat over medium heat, stirring occasionally, until the sugar is completely dissolved. Remove from heat and let it cool to room temperature.
In a large pitcher, combine the cooled brown sugar syrup with 1 cup of fresh lemon juice. Stir well to mix.
Add 4 cups of cold water to the pitcher and stir until everything is well combined.
Taste the lemonade and adjust the sweetness by adding more water or lemon juice if desired.
Chill the lemonade in the refrigerator for at least 30 minutes before serving.
Serve over ice cubes and garnish with lemon slices and fresh mint leaves.