Blend the corn and water to a puree and strain using a fine mesh nut milk bag or muslin fabric. Pour half of it into a saucepan and bring to the boil.
Mix the other half with the mung bean starch until the starch is dissolved. Pour into the boiling corn milk in a steady stream, stirring constantly. Let it boil again and then knock the heat down to low. Stir for 3-4 minutes, making sure you scrape the bottom of the pan to avoid burning and sticking.
Pour the hot liquid into a small pan or heatproof bowl and leave to cool. Pop in the fridge, ideally overnight but for at least a few hours.
To serve, invert the pan/bowl over a cutting board or large plate. Slice into cubes and use in your favourite liang fen recipe.