Prepare the tea infusion by placing the dried butterfly pea flowers in a heat-resistant container. Pour hot water (not boiling, as it can make the tea bitter) over the flowers and steep for 5-7 minutes until the water turns a deep indigo blue.
Strain the tea into a separate container, removing all the flower petals. The intensity of color indicates it’s properly steeped—you want a rich, vibrant blue.
Add sweetener to the hot tea and stir until completely dissolved. Taste and adjust sweetness as needed—the floral flavor pairs well with a touch of honey or simple syrup.
Allow the tea to cool to room temperature, then refrigerate for at least 30 minutes until thoroughly chilled. You can prepare this a day ahead for convenience.
Fill tall glasses with ice, filling them about halfway. The ice not only keeps your drink cold but creates beautiful swirling effects as the liquids mix.
Pour the chilled blue tea over the ice, filling the glasses about ⅔ of the way up. If using vanilla extract, add it now and gently stir.
Slowly pour the milk into each glass, watching as it creates beautiful blue and white swirls through the ice. Leave some space at the top of each glass.
For the color-changing magic, squeeze a lemon or lime wedge into the drink and watch as the blue transforms to purple, starting where the citrus touches the tea.
Garnish with mint leaves if desired, and serve immediately with a reusable straw for stirring and sipping.