Preheat the oven to 350 degrees F.
Place butter in 13 by 9-inch baking dish. Place dish in oven to melt butter. Mix flour, baking powder, and salt in large bowl. Stir in milk and sugar to form batter. Using oven mitts, remove hot baking dish from oven. Pour batter into baking dish. Spoon peaches and any peach juices evenly over batter. Bake until batter rises and browns on top, about 30 minutes.