Gradually mix the water into the corn starch until you get a smooth, lump-free mixture. If desired, add a little sugar to taste.
Transfer the mixture to a pot, and stir continuously over medium-low heat until it thickens to a smooth, custard-like consistency.
Add a little water around the sides of the pot, cover, and simmer for about 10 minutes
Stir well, and test for doneness by placing a small portion in cold water; if it sets firmly after cooling, the agidi is ready.
Transfer the mixture into containers or wrap in leaves, then allow it to cool completely and set before serving.