How to Make It
Light a grill or preheat a grill pan. Brush the corn and onion slices with the olive oil and grill over moderately high heat until charred in spots but still slightly crisp, about 7 minutes. Let cool slightly, then cut the kernels from the cobs and coarsely chop the onion.
In a medium bowl, mix the sour cream with the lime juice, chopped chipotle chiles and sliced scallion and stir in the charred corn and onions. Season the corn salad with salt and pepper and serve immediately.