Sift together flour, baking powder, soda and salt. Add nuts; mix well and set aside. Melt butter in saucepan and remove from heat. (if margarine is used, add 1 tablespoon hot water.) Add brown sugar and beat well. Let cool. Add egg and vanilla and blend. Add flour mixture, a small amount at a time, mixing well after each addition. Spread in greased 8 x 8 inch pan. Sprinkle chocolate chips over top. Bake at 350° for 20-25 minutes. Do not overbake. Cool in pan and cut in squares. If doubling recipe, bake in 9 x 12 inch pan.