In a small heavy saucepan, melt butter. Stir in brown sugar until dissolved; remove from the heat. Stir in brandy; set aside.
Place plank on grill over direct medium heat. Cover and heat for 3 minutes or until light to medium smoke comes from the plank and the wood begins to crackle. (This indicates the plank is ready.)
Place peaches on plank. Grill, covered, over medium heat for 20-23 minutes or until tender, brushing occasionally with brandy sauce. Top each peach half with a scoop of ice cream; drizzle with remaining brandy sauce.