The best way I have found is to soak the ears in husk for several hours before grilling. This lets the husk soak lots of water. Then place the corn, still in husk, on a hot grill for about 10 minutes, ~1/4 turn, 10 minutes, turn... until the husk gets brown, even burnt.
You should be able to tell when the corn is cooked by the smell. The sugars in the corn will start to caramelize and brown in the husk and it will give off a delicious caramel smell. You can check them by peeling down the husk to make sure that they are cooking well.
Times will depend on your grill and how much patience you have. In general, it is difficult to overcook. You want to watch out for drying, but that usually takes a while if you soak the ears beforehand.
Foil is a poor substitute for the natural wrapper. The husk both protects the cob from too much direct heat as well as holding water close to the cob to gently steam the kernels. And its just prettier with the browned and burnt husk, au natural.
There is always a debate on in-the-husk versus out-of-the-husk with roasted corn, but I fall firmly on the out-of-the-husk side of the debate. When you roast corn in the husk, the steam that is created stays largely next to the kernels. When you remove the husk, your corn is cooked with dry heat, which provides a really nice texture that has the significant difference from boiling that you're looking for.
Editing to add: the reason this prevents development of 'roasted' flavours is that dryness is needed for caramelization processes to occur. Excess moisture prevents browning from happening, and either the husk or the tinfoil will trap too much steam; you are essentially steaming the corn (wet cooking) as opposed to roasting it (a dry method).
To keep the kernels from completely drying out while still charring nicely, slather with softened butter and season to your preference. You can also use a Mexican Corn-style sauce.
I would also use the broiler to simulate more of the kind of heat a grill provides. Using the broiler (set to high) you only need to cook for a few minutes until you reach the desired char - ten or so.
Best Answer
The best way I have found is to soak the ears in husk for several hours before grilling. This lets the husk soak lots of water. Then place the corn, still in husk, on a hot grill for about 10 minutes, ~1/4 turn, 10 minutes, turn... until the husk gets brown, even burnt.
You should be able to tell when the corn is cooked by the smell. The sugars in the corn will start to caramelize and brown in the husk and it will give off a delicious caramel smell. You can check them by peeling down the husk to make sure that they are cooking well.
Times will depend on your grill and how much patience you have. In general, it is difficult to overcook. You want to watch out for drying, but that usually takes a while if you soak the ears beforehand.
Foil is a poor substitute for the natural wrapper. The husk both protects the cob from too much direct heat as well as holding water close to the cob to gently steam the kernels. And its just prettier with the browned and burnt husk, au natural.