Grease a 13x9x2 inch baking pan, preheat oven to 350 ℉. In medium bowl combine flour, baking powder and salt. Melt butter, stir in sugar, add eggs and vanilla, beat lightly until just blended (do not over mix). Stir in flour, chocolate chips and nuts. Spread batter in pan, bake for 25 minutes. Cut into bars while still warm.