1. Heat a skillet over medium-high heat. Add the corn and cook, turning occasionally, until charred in spots, about 8-10 minutes. Remove from heat and let cool.
2. Cut the corn kernels off the cob and transfer to a large bowl.
3. In a small bowl, mix together the mayonnaise, sour cream, lime juice, chili powder, salt, and pepper.
4. Pour the dressing over the corn and toss to coat. Add the cotija cheese and cilantro, and mix well.
5. Serve immediately or refrigerate until ready to serve.