Sift together flour, baking powder, baking soda, cinnamon, cloves, mace, salt and allspice. Cream butter until light; gradually add sugar. Add egg and beat well. Add molasses, flour mixture, raisins and nuts. Mix well. Spresd evenly in greased 8 x 12 inch pan. Bake at 350 degress for 20-25 minutes. Cool completely. Cut into 16 rectangles. Wrap tightly in plastic. Store 24 hours before serving.