Dried butterfly pea flowers naturally dye water blue, but when you add citric acid, it turns purple. That’s why the lemon juice comes at the end of the process. If you’re serving a crowd, you could even bring out shot glasses of lemon juice (or a bunch of lemon halves in a bowl) and let your guests add their own. It really is fun to watch the drink transform. From the book, Good Drinks by Julia Bainbridge. Recipe by Nick Wiseman, Little Sesame, Washington, D.C.
NOTE: The chefs at Little Sesame order Doi Thai–brand butterfly pea flowers through Amazon. Wherever you buy them, they’re likely coming from Thailand, where they’re grown, so it might take them some time to arrive at your doorstep. Plan accordingly! —Food52
Toast the coriander seeds in a small sauté pan over medium-low heat, stirring frequently to prevent burning, about 3 minutes. Transfer the seeds to a plate and let cool completely. Crack in a mortar and pestle (or nestle the seeds in a kitchen towel and crush them with a heavy pan).
Combine the dried flowers, sugar, and coriander seeds in a large heatproof bowl or pitcher. Pour the just-boiled water over the ingredients and stir, then allow them to steep for 30 minutes. Fine-strain, discard the solids, and let the tea cool to room temperature, then cover and refrigerate until chilled, about 2 hours. Store in an airtight container in the refrigerator for up to 1 week.
To serve, divide the tea among 6 glasses filled with ice. Add 1 1/2 teaspoons of the lemon juice to each glass. (You could add all 3 tablespoons of lemon juice to the tea base at once, for ease, but like I said previously, it’s fun to let your guests add their own!)