Prepare the ingredients.
Add the butterfly pea flowers into a heat-resistant bowl. Pour hot water and submerge the flowers and give a gentle stir. Set it aside for 10 minutes.
Add the rice to the detachable rice pot, or basin. Add water to the rice while gently agitating them. Drain the water. Fill the rice pot with water once and drain it again. If using a basin, transfer the rice into the rice pot. Set it aside.
After 10 minutes, stir the flowers in the hot water, gently pressing them to extract more natural colouring. Remove the flowers from the bowl and discard them.
Pour the flower water into the rice pot, over a strainer to remove any debris, and add additional water until there is sufficient to cook the rice. Cover the lid and cook the rice.
Meanwhile, prepare the vegetables. Remove the tips of the long beans on both ends, and cut them into three sections. Align the ends on one side and slice them thinly. When done, set the aside.
Next, peel the mango with a peeler. Then, with one hand holding up the mango and the other holding the knife, carefully chop the mango, while rotating it. When the incisions have been made all around the mango, guide the knife with the index finger, and carefully slice the strips off the mango. Repeat until you are left with the seed. Discard the seed and set the mango strips aside.
Slice the white cabbage into thin strips, as though making shredded cabbage. Then, cut the strips into 3 parts to make them shorter. Set them aside. Repeat with the purple cabbage.
Check on the rice. Once it is cooked, open the cover and gently stir the top to fluff up the rice. Cover the pot and set it to keep warm.
Then, remove the stalks from the chillies. Chop them finely and set them aside.
Slice the torch ginger flowers thinly, stopping at the part of the stem that is fibrous. Discard the stems. Then, cut the flower strips into 3 to make them shorter. Set them aside.
Lastly, pluck the Vietnamese basil leaves from their stems. Discard both the stems and yellow leaves. Roll the leaves and slice them thinly. Set them aside.
To assemble the Khao Yum, stir the blue rice a little. Gently pack the fluffy rice into a small bowl. Then place it upside down onto the dinner plate, tapping the bowl a few times to release the rice. Add each of the ingredients around the plate, according to the measurements, increasing or decreasing the amount according to preferences. For the Budu sauce, serve about 1 tbsp in a small saucer. Serve with all of the prepared vegetables and condiments. Optionally, serve with a hard-boiled egg per serving.
To eat, pour about half of the Budu sauce all over the rice and vegetables. If serving with an egg, cut it up into pieces with a spoon. Then, mix them until well combined, or until they resemble a colourful salad, and enjoy. Add more Budu sauce or any other condiment, according to taste.