One to two hours before barbecuing, soak the Cedar Planks in Stout.
Combine all marinade ingredients in a small bowl. Place salmon in a glass bowl, pour the marinade mixture over top, cover with cling film and if desired marinate for 5 minutes.
Pre-heat the barbecue to medium or about 180˚C / 350˚F.
Meanwhile, prepare the apple and fennel slaw.
In a bowl combine the mayonnaise, crème fraîche, cider vinegar and the salt and whisk to combine. Taste and adjust the seasonings if necessary.
In a second bowl, combine the green cabbage, carrot, shallot, fennel and apple matchsticks. Drizzle the dressing over and stir to combine. Cover and set aside ready to serve.
Then, lay the Planks on the barbecue in a single layer so they are in contact with the grill grates. Allow a little space on the sides for heat and air to flow.
Place the salmon skin-side down in a single layer on top of the cedar planks. Place the lid back on the barbecue and leave to cook for 12 - 15 minutes or until when it is uniformly pink in the center.
Tip; Cedar planks can be re-used until they become overly charred, cracked, or impossible to clean. Just scrub off the skin as you would any other dish and allow them to dry until their next use.