Combine first 3 ingredients in a large bowl; stir gently. Spoon into a 9-inch square pan.
Combine flour, baking powder, and salt in a small bowl; set aside. Combine butter and next 4 ingredients in a large bowl; stir well. Add flour mixture, and stir well. Pour batter over fruit. Bake at 350° for 40 minutes or until golden and a wooden pick inserted in center comes out clean. Sprinkle powdered sugar over cobbler before serving, if desired. Serve warm.