Prepare the Simple Syrup:
Combine 1 cup of granulated sugar and 1 cup of water in a small saucepan.
Heat over medium heat, stirring constantly, until the sugar is completely dissolved. Do not boil.
Remove from heat and let cool completely. Add lemon zest to the syrup while it cools for extra flavor, if desired.
Juice the Lemons:
Wash the lemons thoroughly.
Roll the lemons firmly on the countertop to help release more juice.
Cut the lemons in half and squeeze them to extract about 1.5 to 2 cups of fresh juice. Strain out any seeds and excess pulp if desired.
Assemble the Lemonade:
In a large pitcher, combine the cooled simple syrup and the fresh lemon juice.
Add the remaining 4 cups of cold water.
Stir well to combine.
Taste and adjust sweetness or tartness if needed by adding a little more sugar (dissolved in a small amount of hot water first) or lemon juice.
Serve:
Fill glasses with ice cubes.
Pour the prepared lemonade over the ice.
Garnish with lemon slices or mint sprigs, if desired.