Preheat your grill to medium-high heat. Husk the corn and brush the ears lightly with oil to prevent sticking. Place the corn directly on the grill grates, turning occasionally, until evenly charred and smoky, about 10-12 minutes. You'll see the kernels develop dark grill marks and some blistering.
While the corn is grilling, combine the mayonnaise, lime juice, melted butter, chili powder, and chopped cilantro in a bowl. Whisk everything together until smooth and fragrant. This sauce will be creamy with a hint of smoky spice and citrus.
Once the corn is well charred and tender, remove it from the grill and transfer to a serving platter. Use a basting brush or spoon to generously smear the smoky mayo sauce all over the hot kernels, ensuring an even coating that drips down the sides.
Sprinkle the crumbled cotija cheese generously over the coated corn, letting it stick to the sauce and creating a salty, crumbly topping. Add extra chili powder if you like more heat, and finish with additional cilantro if desired.
Serve the Mexican street corn immediately while hot, with the sauce, cheese, and charred bits providing a messy, flavorful bite. Enjoy the contrast of smoky, creamy, and crunchy textures in each mouthful.
