Combine the heavy cream and sugar in a sauce pot. Shear in the agar-agar and the gellan gum using a handheld blender.
Switch to a whisk and bring the mixture to a boil. Boil for 5 seconds, and then take off the heat. Let sit for about 1 minute. This helps reduce the amount of bubbles in the cream. Portion into the letter molds (see Resources) and let set in the refrigerator. Keep in the molds until ready to finish the cake. Discard after 3 days.