If making in a blender, place sour cream, cilantro leaves, chopped garlic clove, lime zest and juice, and a pinch of Kosher salt in the bowl of a blender, then process until very smooth.
Preheat a grill over medium-high heat. When very hot, grease the grill grates with grill spray, then carefully add the corn. Cook, turning, occasionally.
Gently pull down the husk on each ear of corn. You can either remove them completely, or simply fold them over. Brush the corn with a little melted butter, then return to the grill. Cook, until the corn is blistered and charred a little. Transfer to a serving tray.
Drizzle the cilantro crema on top of the corn, then sprinkle with crumbled cotija, as much Cayenne pepper as you like, and lots of fresh cilantro. Serve immediately.