Preheat the barbecue. In a small bowl, mash together the butter with half the chopped chilli, the garlic, coriander, lime zest and cayenne. Spoon onto a sheet of cling film and roll into a sausage. Chill for 30 minutes, until firm.
Bring a large pan of water to the boil. Add the cobs of corn and cook for 6 minutes until just tender. Drain.
Brush the corn with the oil, season with freshly ground black pepper and barbecue for 5-6 minutes, turning to char on all sides.
To serve, squeeze over the lime, scatter with the remaining chopped chilli and top with a slice of the spiced butter to melt on top.