Preheat oven to 375°. In a large bowl, stir together all filling ingredients expect peaches. Fold in and gently stir in peaches once other ingredients are well combined. Pour filling into a 13 x 9" baking pan. In another bowl, combine cobbler gluten-free flour, sugar, baking powder and salt. Cut butter in until crumbly. Gently stir in egg and milk until just moistened. Crumble this mixture over the filling and top with remaining 4 T sugar. Bake 45 minutes or until golden brown with bubbly edges.