Heat oven to 350°. Mix flour, brown sugar, cocoa, baking soda and salt with fork in ungreased square pan, 8x8x2 inches. Or a round pan. Mix in remaining ingredients except chocolate chips. Sprinkle chocolate chips over batter. Bake 35 to 40 minutes or until toothpick inserted in center comes out clean. Sprinkle with powdered sugar if desired.