Bring a large saucepan of salted water to the boil. Plunge in the corn cobs and cook for 5 mins until slightly tender, then drain. Can be done a day ahead – put the corn in a roasting tin, cover and chill until needed.
Season the corn, put on a hot barbecue and cook for 5 mins, turning regularly until it begins to blister and some of the kernels have popped and charred in places. Alternatively, heat a griddle pan over a high heat and griddle the corn for 4-5 mins each side for a similar effect.
Brush on all sides with the melted butter, then scatter over the Parmesan and some black pepper.