Soak the hoary basil seeds ( hạt é ) in 100ml of warm water for 3-5 minutes until the seeds rise and have a white film.
Put the seeds and soaked water in the pot, simmer for about 5 minutes.
Dissolve the jelly powder ( rau câu ) with 800ml of water. Pour 1/2 mixture of dissolved jelly powder into a pot of hoary basil seeds, add 15 grams of white sugar, stir for 5 minutes.
Turn off the heat, pour the mixture of jelly and hoary basil seeds (rau câu hạt é) into the jelly mold, let it cool. Put the jelly in the refrigerator for about 30 minutes to freeze.
Add 15 grams of white sugar and yogurt jar into the dissolved jelly remains, put on the stove, stir, cook for about 5 minutes.
Pour this mixture of jelly and yogurt into the jelly mold, freeze until form 2 layers.
For use, just take the jelly (rau câu) out of the mold and enjoy!