In a blender, add the pandan leaves and ¾ cup water. Puree on high speed until a loose paste forms, 5-7 minutes.
Set a fine mesh sieve in a small bowl and pour in the pandan puree; stir and press the puree to extract as much juice as possible. Discard the solids.
Lightly grease a 7-inch round cake pan with nonstick spray, then line the bottom with a circle of parchment paper. Lightly grease the top of the parchment round.
Fill a medium pot with enough water to reach 4 inches up the sides, then set a 9-inch bamboo steamer inside. Add the cake pan to the steamer, making sure the steamer and cake pan are completely level, then set the pot over medium heat (this will preheat the cake pan while you make the batter). Fill a kettle or second medium pot with water and bring to a simmer.
In a large bowl, whisk the rice flour, tapioca starch, and arrowroot starch.
In a medium bowl, use your hands to mix the coconut milk with the palm sugar until fully blended.
Make a well in the center of the flour mixture and pour in 2 cups of the coconut milk mixture. Mix thoroughly with your hands, kneading and squeezing, until the batter feels thick and gluey, about 5 minutes. Add the rest of the liquid in two batches, mixing thoroughly by hand each time.
Divide the batter into two large measuring cups or bowls (3 cups of batter per container). Add ½ cup of the pandan juice and the food coloring (if using) to one bowl and the jasmine tea to the other, stirring each mixture well.
Pour ¾ of a cup of the green batter into the preheated pan. Dry off the underside of the steamer lid (to avoid any water dripping into the mixture), then replace it, and cover the pan with a lid. Steam the first layer over medium heat until set, slightly translucent, and firm to the touch (it will still be slightly tacky), 8-10 minutes. Repeat the process with a layer of the white batter, cooking for 10-12 minutes.
Continue steaming one layer at a time, alternating colors for at least 5 layers or as many as your pan can hold, ending with a pandan layer. Make sure each layer is thoroughly cooked before adding the next. Keep an eye on the water level and top it off from the simmering kettle as necessary. (The cooking time for each layer will increase slightly as the khanom chan gets thicker.) Remove the covered pan from the heat and let the khanom chan cool completely at room temperature.
Lightly grease a large plate with nonstick spray. Invert the khanom chan onto the plate but do not remove the cake pan. Wrap the inverted cake pan and plate tightly with plastic wrap and refrigerate 8 hours or overnight in the refrigerator.
Unwrap the khanom chan and turn over the cake pan (the khanom chan will still remain inside). Use a sharp paring knife to loosen it from the sides of the pan, then carefully peel the cake out onto the plate or a cutting board. Use an oiled knife to slice the khanom chan into 1 ½ inch diamonds or squares. Serve immediately or store in an airtight container in the refrigerator for up to 1 week.