Sweet Tomato and Peach Cobbler

Name: Sweet Tomato and Peach Cobbler
Ingredients: For the tomatoes and peaches; 8 large plum tomatoes; 6 large yellow peaches; 3 tablespoons butter; 1/2 cup granulated sugar; 1 tablespoon plus 1 teaspoon cornstarch; 1/4 teaspoon ground cinnamon; 1/8 teaspoon ground cayenne pepper; For the biscuit topping; 1 1/3 cups AP flour; 3 tablespoons granulated sugar plus one extra tablespoon for sprinkling; 1 1/2 teaspoons baking powder; 1/2 teaspoon baking soda; 1/4 cup (1/2 stick) butter; 2/3 cup buttermilk; The tomato- peach mixture