Sift together flour, baking powder, salt and baking soda; set aside.
Cream together shortening/butter and brown sugar in a bowl until light and fluffy, using electric mixer at medium speed. Add eggs, one at a time, beating well after each addition. Blend in vanilla.
Gradually stir dry ingredients into creamed mixture, mixing well. Stir in chocolate pieces (batter may be very stiff). Spread mixture in greased 8-inch square baking dish.
Bake at 325° for 35 minutes, or until no imprint remains when lightly touched with finger. Cool in dish on rack. Cut into 2 inch squares.