If using corn with the husks on, soak the ears in water for at least 30 minutes. This helps the husks retain moisture and allows the corn to cook gently on the grill.
Preheat the grill to medium heat. Place the soaked corn on the grill and cook, turning regularly, until the kernels are tender, about 20 minutes.
Remove the corn from the grill and place it on a clean, flat surface. Carefully make a deep incision through the husks and open them. Fold the husks backward to use as a handle.
Return the corn to the grill. Brush generously with melted butter and continue grilling, turning regularly, until the kernels are beautifully toasted and lightly charred, about 5 to 10 minutes.
Meanwhile, make the sauce. In a bowl, combine the mayonnaise, crema, ½ cup queso fresco, lime juice, chile powder, and chopped cilantro. Stir until smooth and well combined.
Remove the corn from the grill and place it on a serving platter. Spread generously with the sauce and finish with additional crumbled queso fresco, chile powder, and fresh cilantro.
Serve immediately with fresh lime wedges, if desired.