Stir together the ingredients for the chile cream, cover, and refrigerate for at least 30 minutes.
Make the Soup:
Heat a charcoal or gas grill to medium-high heat leaving one area on medium-low heat (if using charcoal, then bank the charcoal to one side of the grill), or preheat the oven to 400°F. Strip away all but the innermost layer of the corn husk, pull back the husk and remove the silk. Put the husk back in place, then cover with room temperature water for 15 to 20 minutes. Remove the corn from the bowl, shaking off any excess water.
Grill the corn and onion until grill-marked on all sides. If using a charcoal grill, move the corn and onion to the cooler side of the grill; if using a gas grill, lower the heat to medium-low. Close the lid and grill-roast the vegetables until the onion is soft and deeply browned and the corn kernels are visible beneath the husk, about 15 minutes.
If using an oven, roast the corn and the onion on a rimmed baking sheet, cut side up, until the onion is soft and the corn husk is brittle and fragrant, 30 to 40 minutes.
Once the corn is cool enough to handle, discard the corn husks. Slice the kernels off the cobs into a large bowl; you should have about 4 cups. Holding 1 cob over the bowl with the kernels, use the spine of a chef’s knife to scrape any remaining pulp from the cob. Slice the onion into quarters.
In the blender, place the chicken stock, followed by 3½ cups of the corn, the onion, and garlic. Select the SOUP setting. Once the cycle finishes, remove the emulsion cup and add the cream and the remaining corn kernels. Replace the emulsion cup and select MANUAL/SPEED 2. Pulse to combine. Season with salt and pepper. Divide the soup among bowls. Dollop chile cream on the top and serve.