Preheat oven to 350°.
Place potatoes on oven rack or a baking sheet coated with cooking spray. Bake at 350° for 50 minutes or until tender. Cool. Peel potatoes and mash. Stir in syrup,1 tablespoon brown sugar, and salt.
Spread potato mixture into an 11- x 7-inch baking dish coated with cooking spray. In a small bowl combine walnuts, 1 tablespoon brown sugar, and butter. Sprinkle walnut mixture over potatoes; broil 2 to 4 minutes or until nuts are lightly browned.