Heat oven to 400° F. Place the peach halves, cut-side up, in a baking dish. Sprinkle each half with 1/2 tablespoon of brown sugar, 2 tablespoons of granola, and 2 pieces of butter. Bake until the peaches are soft and the granola begins to brown, about 15 minutes. Transfer to individual plates, spooning the juices in the dish over each peach half. Serve with the ice cream (if desired).