Preheat your grill to medium-high heat until hot and slightly smoky.
Place the ears of corn directly on the grill grates, turning occasionally to develop even charred spots and blackened edges, about 8-10 minutes.
While the corn grills, whisk together mayonnaise, lime juice, melted butter, and chili powder in a bowl until smooth and well combined.
Once the corn has nice charred marks and is cooked through, remove it from the grill and let it cool slightly, just enough to handle.
Use a basting brush or spoon to generously coat each ear of corn with the spicy mayo sauce, allowing it to drip into the charred crevices.
Sprinkle crumbled Cotija cheese evenly over the coated corn, pressing gently so it adheres to the sauce.
Finish by sprinkling chopped cilantro over the top, and squeeze fresh lime juice over each ear for an extra zing.
Serve immediately with plenty of napkins, enjoying the crispy char, creamy coating, and lively flavors in every bite.