Soak plank in water to cover 1 hour; drain.
Stir together horseradish and next 7 ingredients in a small bowl.
Rub plank with olive oil. Place fillets on plank; sprinkle with Creole seasoning. Top each fillet with horseradish mixture.
Bake at 400° for 14 minutes or until fish flakes with a fork. Serve with Butter Sauce, and garnish, if desired.