Rinse the plank with water and soak in water for at least 2 hours. For extra flavor, try soaking the plank in a mixture of water and apple cider or wine. (If needed, place a weight on top of the plank to keep it submerged in the liquid. A can of beans works great for this task!) A large roasting pan or the kitchen sink is a great place to soak.
Preheat grill on medium-heat for 10 minutes, or until grill reaches 350°F.
Rinse salmon in cold water, and then pat dry with paper towel. Season with salt and pepper to taste.
Pat the plank dry and lightly brush one side with olive oil.
Place salmon skin-side down on the oiled side of plank. Place plank directly on grill. Cover the grill, and cook for 13-17 min depending on size of salmon filet. Salmon is done when it is fully pink in the center, or when an instant-read thermometer reads 135F. Fully cooked salmon will also flake easily when scraped with a fork. The salmon does not need to be flipped while grilling. Note: keep a close eye on the plank once it starts to smoke to ensure that it does not catch on fire. A spray bottle of water next to the grill is quite helpful to keep the plank from catching on fire!
Remove skin from salmon. Sprinkle lemon juice on top and garnish with Dill Sauce. Serve hot.
Combine all of the ingredients for the Dill Sauce in a medium bowl and stir together.
Using a mini-food processor or immersion blender, blend the sauce until it reaches a smooth consistency.