Heat coconut oil in a Dutch oven or heavy-bottomed pot over medium heat. Add onions and saute until tender and translucent, about 8 minutes. Add garlic, curry powder and tomato paste and saute to toast the curry powder and warm the tomato paste, about 2 minutes. Add corncobs, half the corn kernels, chicken stock, coconut milk, tamarind paste, brown sugar and salt. Stir to combine, bring to a low boil and reduce heat to a simmer. Simmer for 10 minutes, then remove cobs and discard. Transfer, in batches, to a blender and blend until completely smooth. (See Cook's Note.)
Return soup to the pot and bring back to a low simmer. Add shrimp, lime juice and remaining corn. Simmer until shrimp is just cooked through, 3 to 4 minutes. Garnish with cilantro and Fresno chile and serve.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.