Place the chopped pandan leaves and 250 ml water into a blender. Blend on high for 90 seconds until the leaves are fully broken down and the liquid is a deep green.

Pour the mixture through a fine-mesh sieve set over a bowl, pressing the pulp firmly with a spoon to extract all the juice. You should get about 200 ml of bright green pandan juice. Discard the pulp.

Combine the pandan juice, 300 ml water, agar agar powder, and caster sugar in a medium saucepan. Stir well to disperse the agar powder before turning on the heat.

Heat over medium heat, stirring constantly, until the mixture comes to a gentle boil and the sugar has fully dissolved, about 5 to 7 minutes. Reduce to low and keep warm.

Pour the pandan mixture into your lightly wetted jelly mold or dish in an even layer. Tap the mold gently on the counter twice to release any air bubbles.

Leave the pandan layer to set at room temperature for 20 to 25 minutes. It should be firm to the touch but slightly tacky on the surface - not fully rigid.

While the pandan layer is setting, combine the coconut milk, 150 ml water, agar agar powder, sugar, and salt in a second saucepan. Stir to combine before heating.

Heat over medium-low heat, stirring gently and continuously, until the mixture is steaming and the sugar has dissolved completely, about 6 to 8 minutes. Do not bring to a rolling boil or the coconut milk may split. Remove from heat.

Let the coconut mixture cool for 3 to 4 minutes, stirring occasionally, until it no longer feels scalding when tested on your wrist. It should still be liquid and pourable.

Check the pandan layer - it should be set but still tacky. Pour the coconut mixture slowly over the back of a spoon held just above the pandan surface so it lands gently without breaking through.

Let the full mold sit undisturbed at room temperature for 10 minutes, then transfer carefully to the fridge. Chill uncovered for the first 30 minutes, then cover loosely with plastic wrap.

Chill for at least 3 hours, or overnight for best results, until the cake is completely firm throughout.

Run a thin knife or offset spatula around the inside edge of the mold to break the suction. Place a flat serving plate face-down over the mold, then flip both together in one confident motion.

Lift the mold away gently. If the cake doesn't release immediately, leave it inverted for 30 seconds - gravity will do the work.

Slice into rectangles or diamond shapes with a sharp knife wiped clean between cuts for the neatest edges. Serve cold.