Place 1 cup (about 120 grams) tapioca starch in a bowl. Pour in 1/3 cup (about 100 ml) hot butterfly pea flower water with 1 tablespoon sugar, stir until dissolved, then knead into a dough. Roll into small balls, boil until they float, then soak in the cooking water to keep the pearls soft. Rinse with water to prevent sticking.

Make a sugar syrup and add the tapioca pearls. Bring to a boil, then turn off the heat and let the pearls soak in the syrup. Dice the water chestnuts, toss with sugar and a little pink food coloring, then cook in a pan until dry.

Transfer the water chestnuts to a bowl, add tapioca starch, and toss to coat evenly. Boil water and cook the coated water chestnuts until they float, then transfer to an ice water bath. To prevent sticking, soak the water chestnuts in sugar syrup like the tapioca pearls.

Dissolve the grass jelly powder in 4 1/4 cups water (about 1 liter), add 2 tablespoons sugar, bring to a boil, then pour into a mold and let cool. Refrigerate until set. When ready to serve, cut the jelly into pieces with a wavy knife for a decorative look.

To make the coconut sauce: combine coconut milk, milk, 2 tablespoons sugar, and 2 teaspoons tapioca starch. Stir until dissolved, then bring to a boil. To serve, add a little of each component to a glass, top with ice, and enjoy this refreshing dessert with your family.