Prepare the butterfly pea infusion by bringing 2 cups of water to a simmer in a small pot. Remove from heat, add the dried butterfly pea flowers or tea bags, and let steep for 5-10 minutes until the water turns a deep blue color. Strain and set aside to cool completely.
Make a simple syrup by combining the sugar and 1 cup of water in a small saucepan. Heat over medium heat, stirring occasionally until the sugar completely dissolves (about 3-5 minutes). Remove from heat and allow to cool.
Reserve half of the lemon juice (about ½ cup) in a separate container for the color-changing magic later. This is the crucial ingredient that will trigger the transformation.
Prepare the base lemonade by combining the butterfly pea infusion, the remaining ½ cup of lemon juice, simple syrup, and cold water in a large pitcher. Stir well—the mixture should be a beautiful blue color at this stage.
Chill the lemonade thoroughly in the refrigerator for at least 1 hour. For an extra magical touch, make ice cubes using some of the butterfly pea tea to prevent dilution when serving.
Serve the magic show by pouring the blue lemonade into clear glasses filled with ice. At the table, pour a small amount of the reserved lemon juice into each glass and watch as the lemonade transforms from blue to purple before your eyes!
Garnish each glass with a lemon slice and mint leaves if desired, then serve immediately while the color transition is still vivid.