Slice the grass jelly according to your preference. For classic cubes, cut the jelly into uniform 0.5-inch pieces. If you prefer thin, slurpable strips, grab a sharp julienne peeler and gently shave the jelly into long, delicate strands.
Place a pan or pot over low heat. Add the natural cane sugar, pandan leaves, and water. Stir gently until the sugar completely dissolves.
In a mixing bowl, add your grass jelly cubes or strips. If you have grass jelly juice (often inside the bag with fresh grass jelly), pour it over the jelly.
Pour the sugar syrup from step 2 over the jelly.
Allow the mixture to cool at room temperature for about 10 minutes.
Fill a glass with ice, then pour the cooled liquid mixture over it. Top with extra jelly if you like, and sprinkle with optional brown sugar. Serve with a straw and a spoon for scooping the jelly cubes. Enjoy!