1. Immerse and soak plank in water 1 hour; drain.
2. Preheat grill to medium-high.
3. Place plank on grill rack; grill 3 minutes or until lightly charred. Sprinkle fillets with pepper and salt. Carefully turn plank over using sturdy long-handled tongs. Place fillets, skin-side down, on charred side of plank. Grill 12 minutes or until desired degree of doneness.
4. Melt butter in a small skillet over medium-high heat. Add leek and shallots; sauté for 2 minutes. Stir in grapes and olives; remove from heat. Stir in vinegar. Serve with salmon.