Put the coconut, salt, and hot water in a blender or mini food processor and set aside to soak for 5 minutes.
In a small skillet or sauté pan, heat the coconut oil over medium-high heat. Add the curry leaves, urad dal, if using, mustard seeds, serrano chile, and ginger-garlic paste; stir for 30 seconds, then remove from the heat.
Blend or process the coconut and water until smooth, then transfer to a bowl and stir in the oil and seasonings. Add more salt, if needed. Cover and refrigerate until evening.
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