If your sweetcorn is without leaves and you are in a hurry, bring a big pot of water to the boil. Add the corn and boil until just tender (about 10 minutes). Brush with oil, season and set the corn on the bars of a barbecue. Let it get a lovely charred appearance, turning it round every so often, then serve.
If you want to go the purist route, buy your sweetcorn with leaves on. Pull the leaves back (but not off) and pull out and discard the silky threads underneath. Fold the leaves back in place, twisting them together at the end. You won’t need oil or seasoning. Wrap in foil, or cook as they are, burying them in the barbecue embers for about 40 minutes.