Preheat grill to medium-high heat (about 400°F). Brush 4 ears fresh corn with melted butter and sprinkle with kosher salt.
Grill corn for 10-12 minutes, turning every 2-3 minutes, until charred spots form all over and kernels are tender but still crunchy.
While corn grills, whisk together 1/3 cup mayonnaise, 1/4 cup Mexican crema, lime juice, 1/4 teaspoon garlic powder, and 1/4 teaspoon cayenne until smooth.
Brush or spoon creamy mixture generously over warm corn, coating all sides evenly. Immediately sprinkle with 1/2 cup crumbled cotija cheese, pressing gently to adhere.
Dust with 1 teaspoon chili powder, garnish with 2 tablespoons chopped cilantro, and serve with extra lime wedges and hot sauce if desired.