In a large bowl, combine the flour, baking powder, baking soda and salt and mix well. Cut the butter and shortening into small pieces and add to the flour mixture. Using your fingers, work the cold butter and shortening into the flour mixture until it resembles coarse crumbs. Add the egg and the buttermilk and mix into the flour mixture until it is incorporated. Turn the dough out onto a floured surface and knead gently until the dough forms a smooth ball. Place loaf on a lightly greased cookie sheet. Place the loaf in the oven and bake for 40 to 45 minutes or until golden brown.