Preheat the grill to high heat (around 450°F/232°C).
Brush the corn cobs with melted butter using a silicone brush or paper towel, ensuring an even coating.
4 ears fresh corn on the cob
Place the corn on the hot grill, turning occasionally, until the kernels are charred in spots and have a deep golden color, about 8-10 minutes.
While the corn is grilling, whisk together mayonnaise, lime juice, chili powder, and a pinch of salt in a bowl until smooth.
4 ears fresh corn on the cob
Once cooked, remove the corn from the grill and generously spread the mayonnaise mixture over each cob.
4 ears fresh corn on the cob
Sprinkle crumbled cotija cheese evenly over the coated corn, then finish with a drizzle of lime juice and a dusting of additional chili powder if desired.
4 ears fresh corn on the cob