Bring 4 cups of water to a boil in a medium saucepan.
Once boiling, remove from heat and add the black tea bags. Let steep for 5-7 minutes, depending on your desired strength.
Remove the tea bags and stir in the granulated sugar until fully dissolved.
Add the fresh lemon juice and vanilla extract to the sweetened tea, stirring well to combine.
Allow the tea to cool to room temperature, then refrigerate for at least 1 hour to chill.
Serve over ice cubes in tall glasses, garnished with lemon slices and fresh mint if desired.