How to Make It
Soak four 8-by-7-inch cedar planks in water for 2 hours.
Meanwhile, in a medium bowl, combine the salt with the light brown sugar, chopped dill and grated lemon zest. Coat the salmon fillets thoroughly with the rub and arrange them in a large, shallow dish in one layer. Cover and refrigerate the salmon for 1 hour and 30 minutes.
Rinse the salmon and pat dry. Return the salmon to the dish and cover with the sake. Refrigerate for 1 hour, turning the salmon halfway through.
Light a grill, cover and heat for 10 minutes. Grill the cedar planks until grill marks appear, about 30 seconds per side.
Drain the salmon from the sake and pat the fillets dry. Brush the salmon with olive oil and place 2 fillets on each cedar plank, spacing them apart. Top each fillet with a large dill sprig and 2 lemon slices and drizzle lightly with more olive oil.
Turn off half of the burners on the grill. Carefully set two of the salmon-topped planks on the grill over indirect heat. Cover and grill the salmon for 25 to 30 minutes, rotating the planks halfway through, just until the salmon is cooked. Tent the salmon with foil to keep warm. Repeat to grill the remaining salmon. Serve.