Preheat an overhead grill to high or heat up the barbecue.
Brush the corn on the cobs with the melted butter. Place the corn under the grill or on the bbq until well charred, turning so all sides char equally. This should take around 12-16 minutes.
While the corn is cooking, whisk together the sour cream, mayonnaise, and lime juice in a small bowl. Stir through the zest, garlic, and salt to taste.
When the corn is cooked, top the hot corn with the sauce, a liberal sprinkle of the ancho chilli flakes and parmesan.
Finish garnished with coriander and lime wedges.