Preheat oven to 350 degrees F (180 degrees C). Grease a 9×9-inch baking pan.
Measure 1 cup sifted flour. Add baking powder, baking soda, and salt. Sift again. Add 1/2 cup chopped nuts. Mix well and set aside.
Stir the brown sugar into the melted butter and mix well. Cool slightly.
Mix the beaten egg and vanilla into the brown sugar mixture. Add flour mixture, a little at a time, mixing just until combined.
Spread the batter into the prepared pan. Sprinkle 1/2 to 1 cup chocolate chips on top. Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 20 to 25 minutes.