Peel the 3 onions and 5 garlic cloves; roughly chop the onions.

Remove the kernels from 2 ears of sweet corn; set the kernels aside.

Add coriander seeds, cumin seeds, dried red chilies, 2 chopped onions, garlic, fresh coconut, and 1/2 cup water to a blender.

Blend the mixture into a smooth, thick masala paste; scrape down the blender as needed.

Heat 2 tbsp cooking oil in a large saucepan over medium heat; add the mustard seeds.

When the mustard seeds begin to pop, add 12 curry leaves; fry for 20 to 30 seconds.

Add the remaining chopped onion to the saucepan; sauté until soft and lightly golden, about 4 to 5 minutes.

Stir in the blended masala paste; cook it for 3 to 4 minutes until fragrant and slightly thickened.

Add the sweet corn kernels, ground turmeric, red chilly powder, and salt; stir until the corn is evenly coated.

Pour in 1/2 cup tamarind water and the remaining 2 cups water; stir until combined.

Bring the curry to a gentle boil; reduce the heat to maintain a steady simmer.

Simmer the curry for 20 to 25 minutes; stir it after 5 minutes and occasionally afterward to prevent sticking.

Taste the curry and adjust the salt if needed; serve hot with rice or roti.