Grill the shucked corn, turning occasionally until charred spots appear, about 2–3 minutes per side. Do not let it cook too long. You want it to retain a little crunch and juice.
Let the corn cool a little so you can handle it. Cut the corn kernels off the cob and transfer them to a large bowl.
If using frozen corn, microwave for 1–2 minutes until warm.
Add sour cream, mayonnaise (if using), cilantro, garlic, Cotija cheese, lime juice, and chili powder to the bowl with the corn kernels and combine. Adjust seasoning with salt if needed. Cotija is already salty, so go easy on the salt.
Transfer the corn salad to a large platter—or leave it in the same bowl—and sprinkle generously with more Cotija cheese.
Garnish with more chopped cilantro and slices of lime, if desired.
Notes
The full recipe comfortably serves 10 people as a side dish or appetizer.
If you'd prefer to use frozen corn, measure out 4 ½ cups.