The recipe calls for a lot of prep time (up to a year!), and the products are little triangular pyramids sold for $3.75 a bunch at sandwich shops. But hey, if you can make bánh ú tro, you can enjoy it any time of the year without having to wait until the Fifth of Lunar May.
1. Ash water
Use the fine, soft ash from burnt coal, dissolve in water. The common ratio is 50 grams of ash for every liter of water, but it varies depend on how strong the ash is and how strong you want your banh to be. Let the ash collect at the bottom, leaving a clear solution. Sift the solution to get rid of dirt and coal bits.
You can use lime powder instead of ash. White lime gives bánh ú tro the natural green hues of wrapping leaves, red lime gives them reddish amber hues. The mixing ratio is 20 grams/liter for lime powder.
2. Sticky rice
– Use 1-year-old sticky rice. Such grains are more powdery than new sticky rice. Wash sticky rice with cold water, then soak in ash water overnight or until the grains break easily when you press them between two fingers. Soaking time varies with different ash types and grain types, but beware that grains soaked for too long can make the banh smell like ash.
– After the grains are done soaking, rewash them thoroughly with water and let dry.
3. Sweet filling
Traditional bánh ú tro doesn’t have filling and is eaten with honey or sugar. But bánh ú tro with fillings are arguably tastier than their plain counterparts, and here are a few filling ideas:
– Mung bean paste: split and peeled mung beans are washed and cooked until tender, mashed while it’s still hot and mixed with sugar. The bean-sugar ratio varies to your likings.
– Red bean paste: soak red beans in water overnight to soften them. Wash, cook until tender, mash. In a skillet, add 1 tbs oil and 200g brown sugar for every 500g red bean, stir on low heat until all sugar dissolves. Let cool.
– Grated coconut: boil water and sugar with ratio 1:1 on low heat , stir frequently until all sugar dissolves. Pour the syrup into grated coconut and mix until it becomes a soft sticky ball.
4. Wrapping bánh ú tro
– Use bamboo leaves (about 5-6 cm wide and 30 cm long) or banana leaves cut into similar size. Wash the leaves clean and let dry.
– Bend one end of a leaf into cone shape. Use 2-3 leaves to increase the banh size.
– Put in 2-3 teaspoons of sticky rice for the plain kind. Or 1 tsp sticky rice, followed by 1 tsp filling, then 1 tsp sticky rice on top for the sweet kind.
– Wrap the remainder of the leaf tightly around and over the cone until all faces are covered.
– Tie it up with a nylon string. Then tie every ten banh into a bunch with a long string to easily pull in and out of boiling water.
5. Boiling bánh ú tro
– Cover the bottom of a large pot with banana leaves or bamboo leaves to keep banh from sticking to the metal.
– Arrange banh in the pot. Pour water. Water level should be at least 4 inches above the banh. Make sure banh stay submerged the whole time, you can cover banh with a big sieve and a weight on top to keep banh from floating up.
– Boil banh for 45 minutes to an hour (after the water starts boiling). Add more water if the level gets too low.
Submerge cooked banh in cold water for 10 minutes to aid cooling, then hang them dry. Well made ones can last 2-3 weeks at room temperature.
Recipe translated from source.