I first saw this recipe on an episode of River Cottage, it looked amazing but I think that Brandt Berglund and Clare E. Bolsby have trumped Mr. Fearnley-Wittingsall with this recipe from their 1976 publication - "Wilderness Cookbook."
When I tried this method of cooking, I did a whole side of salmon on an offcut of wood. I didn't have any wooden pegs so I used regular nails, and I was fresh out of bear grease so I used butter, a little olive oil and some herbs. I also put a cast iron pan beneath the plank to catch all the goodness that came out which I used to baste the fish and pour over the meat when finished. It took a little over 20 minutes, but it was a big piece of fish.
The finished salmon fell away from the skin and was succulent and moist. Incredibly straight forward and extremely delicious.