Make the simple syrup by combining 1 cup sugar and 1 cup water in a small saucepan. Bring to a boil, stirring until the sugar dissolves completely. Remove from the heat and let cool for about 30 minutes.

While the syrup cools, juice the lemons to yield 1 cup of lemon juice. Strain to remove seeds and excess pulp for a smoother lemonade.

In a large pitcher, combine the cooled syrup, lemon juice, and 4 cups cold water. Stir until well mixed.

Taste and adjust as needed, adding more sugar, lemon juice, or water to balance the sweetness and tartness.

Serve over ice in a pitcher or individual glasses. Garnish with lemon slices and mint leaves, if desired.