Sift together flour, baking powder, soda and salt. Add nuts; mix well and set aside. Melt butter in saucepan; remove from heat. (If margarine is used, add 2 tablespoons hot water.) Add brwon sugar; beat well. Let cool. Add eggs and vanilla; Blend well. Add flour mixture, a small amount at a time, mixing well after each addition. Spread in greased 9x12-inch baking pan. Bake at 180ºC or 20 to 25 minutes. Do not overbake. Cool in pan and cut in squares.
Preparation time: 15 minutes Baking time: 20 to 25 minutes