Rinse the black beans thoroughly, removing any damaged or floating beans. If you have time and aren't in a hurry, soak the beans for 4-5 hours to help them cook faster and softer. Wash the black beans again, place them in a rice cooker, add enough water to cover the beans by about 1 inch (2 finger-widths), and cook for about 20 minutes. Once the beans are soft, pour the cooking liquid into a bowl, leaving just the beans in the cooker. Add rock sugar and light brown sugar to the beans and gently stir to let the beans absorb the sweetness, being careful not to break them.

Prepare the grass jelly according to the instructions on the packet.

To serve, scoop the black bean dessert into a bowl, add grass jelly on top, and drizzle a few drops of banana essence (included in the grass jelly powder packet). Serve chilled!