Soak plank in water for 1-2 hours.
In small bowl, whisk mustard, maple syrup, balsamic vinegar and salt and pepper to taste.
Prepare grill to temperature of 350º.
Wipe plank dry and place on hot grill and close lid.
Heat plank for 3 minutes on one side and then flip and heat another 3 minutes until plank begins to smoke and crackle.
Using tongs, take plank off grill and onto a sheet pan. Arrange salmon on plank and brush it all over with maple mustard sauce. Season with salt and pepper.
Return plank with salmon to the grill with tongs. Close lid and grill until just done, about 10 minutes (about 20 minutes if using a whole piece).
Remove plank and salmon from grill and tent with foil and let rest for 5 minutes. Enjoy.