Cut the corn kernels away from the cob. Add the cobs, 6 cups of water, and the diced potato to a soup pot. Bring to a boil, then reduce heat and simmer 20 minutes. Discard the cobs.

Stir in coconut milk, red curry paste, and half of the reserved corn. Simmer for 5 minutes. Transfer to a blender or food processor and process into a smooth puree.

Return the puree to the pot. Add the remaining corn, cilantro, and shrimp. Simmer until shrimp are cooked through, about 5 minutes. Stir in fish sauce and lime juice. Garnish with jalapeno slices, if desired.