Prepare the cornstarch mixture:
In a bowl, dissolve the cornstarch in 1/2 cup of water to make a smooth slurry. Set aside.

Combine liquids:
In a medium saucepan, combine the coconut milk, sweetened condensed milk, and sugar (if using). Stir over low heat until the mixture is well combined and heated through.

Add the cornstarch mixture:
Slowly pour the cornstarch slurry into the milk mixture, stirring constantly to avoid lumps. Continue stirring over low heat until the mixture thickens and becomes smooth and creamy.

Add corn kernels:
Add the corn kernels to the mixture, stirring them in evenly. Let the mixture cook for another 2-3 minutes until everything is well combined.

Set the mixture:
Pour the creamy mixture into a greased 9×9-inch square pan or individual molds, spreading it evenly. Let it cool at room temperature for 30 minutes, then refrigerate for at least 2 hours to set and firm up.

Top and serve:
Before serving, sprinkle with toasted grated coconut or additional corn kernels for texture and decoration. Slice into squares or serve in individual portions.