Make the Teriyaki glaze by placing all the glaze ingredients into a small saucepan.
Over a high heat on the stove top boil the glaze for 5 minutes or until it starts to thicken and reduce.
Once reduced remove from the heat and set aside to cool completely.
Soak the cedar plank for 60 minutes in cold water with a weight on top to stop it floating.
Place the chicken thighs in a bowl and cover with the cooled glaze. Marinate the chicken for 30 minutes in the fridge.
Once the cedar plank has finished soaking preheat your barbecue for direct cooking.
Once the barbecue is preheated, place the cedar plank directly on the grill. Turn all burners to medium. Leave the plank on the grill for 5 minutes or until it starts to blacken and cinder.
Flip the plank over so the charred side is facing up. Place your chicken thighs directly on the plank.
Leave the burners on medium and cook the chicken for 20-25 minutes or until cooked through.